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<script type="text/javascript" src="_static/codesets.js"></script><div class="section" id="writing-a-contract-test">
<h1>Writing a contract test<a class="headerlink" href="#writing-a-contract-test" title="Permalink to this headline"></a></h1>
<p>This tutorial will take you through the steps required to write a contract test using Kotlin and Java.</p>
<p>The testing DSL allows one to define a piece of the ledger with transactions referring to each other, and ways of
verifying their correctness.</p>
<div class="section" id="testing-single-transactions">
<h2>Testing single transactions<a class="headerlink" href="#testing-single-transactions" title="Permalink to this headline"></a></h2>
<p>We start with the empty ledger:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">CommercialPaperTest</span><span class="p">{</span>
<span class="n">@Test</span>
<span class="k">fun</span> <span class="nf">emptyLedger</span><span class="p">()</span> <span class="p">{</span>
<span class="n">ledger</span> <span class="p">{</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">static</span> <span class="n">net</span><span class="o">.</span><span class="na">corda</span><span class="o">.</span><span class="na">core</span><span class="o">.</span><span class="na">testing</span><span class="o">.</span><span class="na">JavaTestHelpers</span><span class="o">.*;</span>
<span class="kn">import</span> <span class="nn">static</span> <span class="n">net</span><span class="o">.</span><span class="na">corda</span><span class="o">.</span><span class="na">core</span><span class="o">.</span><span class="na">contracts</span><span class="o">.</span><span class="na">JavaTestHelpers</span><span class="o">.*;</span>
<span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">emptyLedger</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span> <span class="c1">// We need to return this explicitly</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>The DSL keyword <code class="docutils literal"><span class="pre">ledger</span></code> takes a closure that can build up several transactions and may verify their overall
correctness. A ledger is effectively a fresh world with no pre-existing transactions or services within it.</p>
<p>We will start with defining helper function that returns a <code class="docutils literal"><span class="pre">CommercialPaper</span></code> state:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>fun getPaper(): ICommercialPaperState = CommercialPaper.State(
issuance = MEGA_CORP.ref(123),
owner = MEGA_CORP_PUBKEY,
faceValue = 1000.DOLLARS `issued by` MEGA_CORP.ref(123),
maturityDate = TEST_TX_TIME + 7.days
)
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="kd">private</span> <span class="kd">final</span> <span class="n">OpaqueBytes</span> <span class="n">defaultRef</span> <span class="o">=</span> <span class="k">new</span> <span class="n">OpaqueBytes</span><span class="o">(</span><span class="k">new</span> <span class="kt">byte</span><span class="o">[]{</span><span class="mi">123</span><span class="o">});</span>
<span class="kd">private</span> <span class="n">ICommercialPaperState</span> <span class="nf">getPaper</span><span class="o">()</span> <span class="o">{</span>
<span class="k">return</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">(</span>
<span class="n">getMEGA_CORP</span><span class="o">().</span><span class="na">ref</span><span class="o">(</span><span class="n">defaultRef</span><span class="o">),</span>
<span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span>
<span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">1000</span><span class="o">),</span> <span class="n">getMEGA_CORP</span><span class="o">().</span><span class="na">ref</span><span class="o">(</span><span class="n">defaultRef</span><span class="o">)),</span>
<span class="n">getTEST_TX_TIME</span><span class="o">().</span><span class="na">plus</span><span class="o">(</span><span class="mi">7</span><span class="o">,</span> <span class="n">ChronoUnit</span><span class="o">.</span><span class="na">DAYS</span><span class="o">)</span>
<span class="o">);</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>It&#8217;s a <code class="docutils literal"><span class="pre">CommercialPaper</span></code> issued by <code class="docutils literal"><span class="pre">MEGA_CORP</span></code> with face value of $1000 and maturity date in 7 days.</p>
<p>Let&#8217;s add a <code class="docutils literal"><span class="pre">CommercialPaper</span></code> transaction:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="n">@Test</span>
<span class="k">fun</span> <span class="nf">simpleCPDoesntCompile</span><span class="p">()</span> <span class="p">{</span>
<span class="k">val</span> <span class="py">inState</span> <span class="p">=</span> <span class="n">getPaper</span><span class="p">()</span>
<span class="n">ledger</span> <span class="p">{</span>
<span class="n">transaction</span> <span class="p">{</span>
<span class="n">input</span><span class="p">(</span><span class="n">inState</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleCPDoesntCompile</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ICommercialPaperState</span> <span class="n">inState</span> <span class="o">=</span> <span class="n">getPaper</span><span class="o">();</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="n">inState</span><span class="o">);</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>We can add a transaction to the ledger using the <code class="docutils literal"><span class="pre">transaction</span></code> primitive. The transaction in turn may be defined by
specifying <code class="docutils literal"><span class="pre">input</span></code>-s, <code class="docutils literal"><span class="pre">output</span></code>-s, <code class="docutils literal"><span class="pre">command</span></code>-s and <code class="docutils literal"><span class="pre">attachment</span></code>-s.</p>
<p>The above <code class="docutils literal"><span class="pre">input</span></code> call is a bit special; transactions don&#8217;t actually contain input states, just references
to output states of other transactions. Under the hood the above <code class="docutils literal"><span class="pre">input</span></code> call creates a dummy transaction in the
ledger (that won&#8217;t be verified) which outputs the specified state, and references that from this transaction.</p>
<p>The above code however doesn&#8217;t compile:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="n">Error</span><span class="p">:(</span><span class="m">29</span><span class="p">,</span> <span class="m">17</span><span class="p">)</span> <span class="n">Kotlin</span><span class="p">:</span> <span class="n">Type</span> <span class="n">mismatch</span><span class="p">:</span> <span class="n">inferred</span> <span class="n">type</span> <span class="k">is</span> <span class="n">Unit</span> <span class="n">but</span> <span class="n">EnforceVerifyOrFail</span> <span class="n">was</span> <span class="n">expected</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nl">Error:</span><span class="o">(</span><span class="mi">35</span><span class="o">,</span> <span class="mi">27</span><span class="o">)</span> <span class="n">java</span><span class="o">:</span> <span class="n">incompatible</span> <span class="n">types</span><span class="o">:</span> <span class="n">bad</span> <span class="k">return</span> <span class="n">type</span> <span class="n">in</span> <span class="n">lambda</span> <span class="n">expression</span> <span class="n">missing</span> <span class="k">return</span> <span class="n">value</span>
</pre></div>
</div>
</div>
<p>This is deliberate: The DSL forces us to specify either <code class="docutils literal"><span class="pre">this.verifies()</span></code> or <code class="docutils literal"><span class="pre">this</span> <span class="pre">`fails</span> <span class="pre">with`</span> <span class="pre">&quot;some</span> <span class="pre">text&quot;</span></code> on the
last line of <code class="docutils literal"><span class="pre">transaction</span></code>:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="n">@Test</span>
<span class="k">fun</span> <span class="nf">simpleCP</span><span class="p">()</span> <span class="p">{</span>
<span class="k">val</span> <span class="py">inState</span> <span class="p">=</span> <span class="n">getPaper</span><span class="p">()</span>
<span class="n">ledger</span> <span class="p">{</span>
<span class="n">transaction</span> <span class="p">{</span>
<span class="n">input</span><span class="p">(</span><span class="n">inState</span><span class="p">)</span>
<span class="k">this</span><span class="p">.</span><span class="n">verifies</span><span class="p">()</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleCP</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ICommercialPaperState</span> <span class="n">inState</span> <span class="o">=</span> <span class="n">getPaper</span><span class="o">();</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="n">inState</span><span class="o">);</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>Let&#8217;s take a look at a transaction that fails.</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span><span class="n">@Test</span>
<span class="k">fun</span> <span class="nf">simpleCPMove</span><span class="p">()</span> <span class="p">{</span>
<span class="k">val</span> <span class="py">inState</span> <span class="p">=</span> <span class="n">getPaper</span><span class="p">()</span>
<span class="n">ledger</span> <span class="p">{</span>
<span class="n">transaction</span> <span class="p">{</span>
<span class="n">input</span><span class="p">(</span><span class="n">inState</span><span class="p">)</span>
<span class="n">command</span><span class="p">(</span><span class="n">MEGA_CORP_PUBKEY</span><span class="p">)</span> <span class="p">{</span> <span class="n">CommercialPaper</span><span class="p">.</span><span class="n">Commands</span><span class="p">.</span><span class="n">Move</span><span class="p">()</span> <span class="p">}</span>
<span class="k">this</span><span class="p">.</span><span class="n">verifies</span><span class="p">()</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleCPMove</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ICommercialPaperState</span> <span class="n">inState</span> <span class="o">=</span> <span class="n">getPaper</span><span class="o">();</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="n">inState</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>When run, that code produces the following error:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>net.corda.core.contracts.TransactionVerificationException$ContractRejection: java.lang.IllegalArgumentException: Failed requirement: the state is propagated
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="n">net</span><span class="o">.</span><span class="na">corda</span><span class="o">.</span><span class="na">core</span><span class="o">.</span><span class="na">contracts</span><span class="o">.</span><span class="na">TransactionVerificationException$ContractRejection</span><span class="o">:</span> <span class="n">java</span><span class="o">.</span><span class="na">lang</span><span class="o">.</span><span class="na">IllegalStateException</span><span class="o">:</span> <span class="n">the</span> <span class="n">state</span> <span class="n">is</span> <span class="n">propagated</span>
</pre></div>
</div>
</div>
<p>The transaction verification failed, because we wanted to move paper but didn&#8217;t specify an output - but the state should be propagated.
However we can specify that this is an intended behaviour by changing <code class="docutils literal"><span class="pre">this.verifies()</span></code> to <code class="docutils literal"><span class="pre">this</span> <span class="pre">`fails</span> <span class="pre">with`</span> <span class="pre">&quot;the</span> <span class="pre">state</span> <span class="pre">is</span> <span class="pre">propagated&quot;</span></code>:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun simpleCPMoveFails() {
val inState = getPaper()
ledger {
transaction {
input(inState)
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this `fails with` &quot;the state is propagated&quot;
}
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleCPMoveFails</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ICommercialPaperState</span> <span class="n">inState</span> <span class="o">=</span> <span class="n">getPaper</span><span class="o">();</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="n">inState</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">failsWith</span><span class="o">(</span><span class="s">&quot;the state is propagated&quot;</span><span class="o">);</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>We can continue to build the transaction until it <code class="docutils literal"><span class="pre">verifies</span></code>:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun simpleCPMoveSuccess() {
val inState = getPaper()
ledger {
transaction {
input(inState)
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this `fails with` &quot;the state is propagated&quot;
output(&quot;alice&#39;s paper&quot;) { inState `owned by` ALICE_PUBKEY }
this.verifies()
}
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleCPMoveSuccess</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ICommercialPaperState</span> <span class="n">inState</span> <span class="o">=</span> <span class="n">getPaper</span><span class="o">();</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="n">inState</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">failsWith</span><span class="o">(</span><span class="s">&quot;the state is propagated&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inState</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">()));</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p><code class="docutils literal"><span class="pre">output</span></code> specifies that we want the input state to be transferred to <code class="docutils literal"><span class="pre">ALICE</span></code> and <code class="docutils literal"><span class="pre">command</span></code> adds the
<code class="docutils literal"><span class="pre">Move</span></code> command itself, signed by the current owner of the input state, <code class="docutils literal"><span class="pre">MEGA_CORP_PUBKEY</span></code>.</p>
<p>We constructed a complete signed commercial paper transaction and verified it. Note how we left in the <code class="docutils literal"><span class="pre">fails</span> <span class="pre">with</span></code>
line - this is fine, the failure will be tested on the partially constructed transaction.</p>
<p>What should we do if we wanted to test what happens when the wrong party signs the transaction? If we simply add a
<code class="docutils literal"><span class="pre">command</span></code> it will permanently ruin the transaction... Enter <code class="docutils literal"><span class="pre">tweak</span></code>:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun `simple issuance with tweak`() {
ledger {
transaction {
output(&quot;paper&quot;) { getPaper() } // Some CP is issued onto the ledger by MegaCorp.
tweak {
command(DUMMY_PUBKEY_1) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this `fails with` &quot;output states are issued by a command signer&quot;
}
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this.verifies()
}
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleIssuanceWithTweak</span><span class="o">()</span> <span class="o">{</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">,</span> <span class="n">getPaper</span><span class="o">());</span> <span class="c1">// Some CP is issued onto the ledger by MegaCorp.</span>
<span class="n">tx</span><span class="o">.</span><span class="na">tweak</span><span class="o">(</span><span class="n">tw</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tw</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getDUMMY_PUBKEY_1</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tw</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tw</span><span class="o">.</span><span class="na">failsWith</span><span class="o">(</span><span class="s">&quot;output states are issued by a command signer&quot;</span><span class="o">);</span>
<span class="o">});</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p><code class="docutils literal"><span class="pre">tweak</span></code> creates a local copy of the transaction. This makes possible to locally &#8220;ruin&#8221; the transaction while not
modifying the original one, allowing testing of different error conditions.</p>
<p>We now have a neat little test that tests a single transaction. This is already useful, and in fact testing of a single
transaction in this way is very common. There is even a shorthand top-level <code class="docutils literal"><span class="pre">transaction</span></code> primitive that creates a
ledger with a single transaction:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun `simple issuance with tweak and top level transaction`() {
transaction {
output(&quot;paper&quot;) { getPaper() } // Some CP is issued onto the ledger by MegaCorp.
tweak {
command(DUMMY_PUBKEY_1) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this `fails with` &quot;output states are issued by a command signer&quot;
}
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this.verifies()
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">simpleIssuanceWithTweakTopLevelTx</span><span class="o">()</span> <span class="o">{</span>
<span class="n">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">,</span> <span class="n">getPaper</span><span class="o">());</span> <span class="c1">// Some CP is issued onto the ledger by MegaCorp.</span>
<span class="n">tx</span><span class="o">.</span><span class="na">tweak</span><span class="o">(</span><span class="n">tw</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tw</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getDUMMY_PUBKEY_1</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tw</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tw</span><span class="o">.</span><span class="na">failsWith</span><span class="o">(</span><span class="s">&quot;output states are issued by a command signer&quot;</span><span class="o">);</span>
<span class="o">});</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="chaining-transactions">
<h2>Chaining transactions<a class="headerlink" href="#chaining-transactions" title="Permalink to this headline"></a></h2>
<p>Now that we know how to define a single transaction, let&#8217;s look at how to define a chain of them:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun `chain commercial paper`() {
val issuer = MEGA_CORP.ref(123)
ledger {
unverifiedTransaction {
output(&quot;alice&#39;s $900&quot;, 900.DOLLARS.CASH `issued by` issuer `owned by` ALICE_PUBKEY)
}
// Some CP is issued onto the ledger by MegaCorp.
transaction(&quot;Issuance&quot;) {
output(&quot;paper&quot;) { getPaper() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this.verifies()
}
transaction(&quot;Trade&quot;) {
input(&quot;paper&quot;)
input(&quot;alice&#39;s $900&quot;)
output(&quot;borrowed $900&quot;) { 900.DOLLARS.CASH `issued by` issuer `owned by` MEGA_CORP_PUBKEY }
output(&quot;alice&#39;s paper&quot;) { &quot;paper&quot;.output&lt;ICommercialPaperState&gt;() `owned by` ALICE_PUBKEY }
command(ALICE_PUBKEY) { Cash.Commands.Move() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this.verifies()
}
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">chainCommercialPaper</span><span class="o">()</span> <span class="o">{</span>
<span class="n">PartyAndReference</span> <span class="n">issuer</span> <span class="o">=</span> <span class="n">getMEGA_CORP</span><span class="o">().</span><span class="na">ref</span><span class="o">(</span><span class="n">defaultRef</span><span class="o">);</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">unverifiedTransaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">,</span>
<span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="c1">// Some CP is issued onto the ledger by MegaCorp.</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Issuance&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">,</span> <span class="n">getPaper</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Trade&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;borrowed $900&quot;</span><span class="o">,</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span> <span class="n">inputPaper</span> <span class="o">=</span> <span class="n">l</span><span class="o">.</span><span class="na">retrieveOutput</span><span class="o">(</span><span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inputPaper</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">()));</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>In this example we declare that <code class="docutils literal"><span class="pre">ALICE</span></code> has $900 but we don&#8217;t care where from. For this we can use
<code class="docutils literal"><span class="pre">unverifiedTransaction</span></code>. Note how we don&#8217;t need to specify <code class="docutils literal"><span class="pre">this.verifies()</span></code>.</p>
<p>Notice that we labelled output with <code class="docutils literal"><span class="pre">&quot;alice's</span> <span class="pre">$900&quot;</span></code>, also in transaction named <code class="docutils literal"><span class="pre">&quot;Issuance&quot;</span></code>
we labelled a commercial paper with <code class="docutils literal"><span class="pre">&quot;paper&quot;</span></code>. Now we can subsequently refer to them in other transactions, e.g.
by <code class="docutils literal"><span class="pre">input(&quot;alice's</span> <span class="pre">$900&quot;)</span></code> or <code class="docutils literal"><span class="pre">&quot;paper&quot;.output&lt;ICommercialPaperState&gt;()</span></code>.</p>
<p>The last transaction named <code class="docutils literal"><span class="pre">&quot;Trade&quot;</span></code> exemplifies simple fact of selling the <code class="docutils literal"><span class="pre">CommercialPaper</span></code> to Alice for her $900,
$100 less than the face value at 10% interest after only 7 days.</p>
<p>We can also test whole ledger calling <code class="docutils literal"><span class="pre">this.verifies()</span></code> and <code class="docutils literal"><span class="pre">this.fails()</span></code> on the ledger level.
To do so let&#8217;s create a simple example that uses the same input twice:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun `chain commercial paper double spend`() {
val issuer = MEGA_CORP.ref(123)
ledger {
unverifiedTransaction {
output(&quot;alice&#39;s $900&quot;, 900.DOLLARS.CASH `issued by` issuer `owned by` ALICE_PUBKEY)
}
// Some CP is issued onto the ledger by MegaCorp.
transaction(&quot;Issuance&quot;) {
output(&quot;paper&quot;) { getPaper() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this.verifies()
}
transaction(&quot;Trade&quot;) {
input(&quot;paper&quot;)
input(&quot;alice&#39;s $900&quot;)
output(&quot;borrowed $900&quot;) { 900.DOLLARS.CASH `issued by` issuer `owned by` MEGA_CORP_PUBKEY }
output(&quot;alice&#39;s paper&quot;) { &quot;paper&quot;.output&lt;ICommercialPaperState&gt;() `owned by` ALICE_PUBKEY }
command(ALICE_PUBKEY) { Cash.Commands.Move() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this.verifies()
}
transaction {
input(&quot;paper&quot;)
// We moved a paper to another pubkey.
output(&quot;bob&#39;s paper&quot;) { &quot;paper&quot;.output&lt;ICommercialPaperState&gt;() `owned by` BOB_PUBKEY }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this.verifies()
}
this.fails()
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">chainCommercialPaperDoubleSpend</span><span class="o">()</span> <span class="o">{</span>
<span class="n">PartyAndReference</span> <span class="n">issuer</span> <span class="o">=</span> <span class="n">getMEGA_CORP</span><span class="o">().</span><span class="na">ref</span><span class="o">(</span><span class="n">defaultRef</span><span class="o">);</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">unverifiedTransaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">,</span>
<span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="c1">// Some CP is issued onto the ledger by MegaCorp.</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Issuance&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">,</span> <span class="n">getPaper</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Trade&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;borrowed $900&quot;</span><span class="o">,</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span> <span class="n">inputPaper</span> <span class="o">=</span> <span class="n">l</span><span class="o">.</span><span class="na">retrieveOutput</span><span class="o">(</span><span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inputPaper</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">()));</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span> <span class="n">inputPaper</span> <span class="o">=</span> <span class="n">l</span><span class="o">.</span><span class="na">retrieveOutput</span><span class="o">(</span><span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="c1">// We moved a paper to other pubkey.</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;bob&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inputPaper</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getBOB_PUBKEY</span><span class="o">()));</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">fails</span><span class="o">();</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
</div>
</div>
<p>The transactions <code class="docutils literal"><span class="pre">verifies()</span></code> individually, however the state was spent twice! That&#8217;s why we need the global ledger
verification (<code class="docutils literal"><span class="pre">this.fails()</span></code> at the end). As in previous examples we can use <code class="docutils literal"><span class="pre">tweak</span></code> to create a local copy of the whole ledger:</p>
<div class="codeset container">
<div class="highlight-kotlin"><div class="highlight"><pre><span></span>@Test
fun `chain commercial tweak`() {
val issuer = MEGA_CORP.ref(123)
ledger {
unverifiedTransaction {
output(&quot;alice&#39;s $900&quot;, 900.DOLLARS.CASH `issued by` issuer `owned by` ALICE_PUBKEY)
}
// Some CP is issued onto the ledger by MegaCorp.
transaction(&quot;Issuance&quot;) {
output(&quot;paper&quot;) { getPaper() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Issue() }
timestamp(TEST_TX_TIME)
this.verifies()
}
transaction(&quot;Trade&quot;) {
input(&quot;paper&quot;)
input(&quot;alice&#39;s $900&quot;)
output(&quot;borrowed $900&quot;) { 900.DOLLARS.CASH `issued by` issuer `owned by` MEGA_CORP_PUBKEY }
output(&quot;alice&#39;s paper&quot;) { &quot;paper&quot;.output&lt;ICommercialPaperState&gt;() `owned by` ALICE_PUBKEY }
command(ALICE_PUBKEY) { Cash.Commands.Move() }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this.verifies()
}
tweak {
transaction {
input(&quot;paper&quot;)
// We moved a paper to another pubkey.
output(&quot;bob&#39;s paper&quot;) { &quot;paper&quot;.output&lt;ICommercialPaperState&gt;() `owned by` BOB_PUBKEY }
command(MEGA_CORP_PUBKEY) { CommercialPaper.Commands.Move() }
this.verifies()
}
this.fails()
}
this.verifies()
}
}
</pre></div>
</div>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="nd">@Test</span>
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">chainCommercialPaperTweak</span><span class="o">()</span> <span class="o">{</span>
<span class="n">PartyAndReference</span> <span class="n">issuer</span> <span class="o">=</span> <span class="n">getMEGA_CORP</span><span class="o">().</span><span class="na">ref</span><span class="o">(</span><span class="n">defaultRef</span><span class="o">);</span>
<span class="n">ledger</span><span class="o">(</span><span class="n">l</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">l</span><span class="o">.</span><span class="na">unverifiedTransaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">,</span>
<span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="c1">// Some CP is issued onto the ledger by MegaCorp.</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Issuance&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">,</span> <span class="n">getPaper</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Issue</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">timestamp</span><span class="o">(</span><span class="n">getTEST_TX_TIME</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="s">&quot;Trade&quot;</span><span class="o">,</span> <span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;alice&#39;s $900&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;borrowed $900&quot;</span><span class="o">,</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">State</span><span class="o">(</span><span class="n">issuedBy</span><span class="o">(</span><span class="n">DOLLARS</span><span class="o">(</span><span class="mi">900</span><span class="o">),</span> <span class="n">issuer</span><span class="o">),</span> <span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="kc">null</span><span class="o">));</span>
<span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span> <span class="n">inputPaper</span> <span class="o">=</span> <span class="n">l</span><span class="o">.</span><span class="na">retrieveOutput</span><span class="o">(</span><span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;alice&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inputPaper</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">()));</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getALICE_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">Cash</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">tweak</span><span class="o">(</span><span class="n">lw</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">lw</span><span class="o">.</span><span class="na">transaction</span><span class="o">(</span><span class="n">tx</span> <span class="o">-&gt;</span> <span class="o">{</span>
<span class="n">tx</span><span class="o">.</span><span class="na">input</span><span class="o">(</span><span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span> <span class="n">inputPaper</span> <span class="o">=</span> <span class="n">l</span><span class="o">.</span><span class="na">retrieveOutput</span><span class="o">(</span><span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">State</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&quot;paper&quot;</span><span class="o">);</span>
<span class="c1">// We moved a paper to another pubkey.</span>
<span class="n">tx</span><span class="o">.</span><span class="na">output</span><span class="o">(</span><span class="s">&quot;bob&#39;s paper&quot;</span><span class="o">,</span> <span class="n">inputPaper</span><span class="o">.</span><span class="na">withOwner</span><span class="o">(</span><span class="n">getBOB_PUBKEY</span><span class="o">()));</span>
<span class="n">tx</span><span class="o">.</span><span class="na">command</span><span class="o">(</span><span class="n">getMEGA_CORP_PUBKEY</span><span class="o">(),</span> <span class="k">new</span> <span class="n">JavaCommercialPaper</span><span class="o">.</span><span class="na">Commands</span><span class="o">.</span><span class="na">Move</span><span class="o">());</span>
<span class="k">return</span> <span class="n">tx</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="o">});</span>
<span class="n">lw</span><span class="o">.</span><span class="na">fails</span><span class="o">();</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="n">l</span><span class="o">.</span><span class="na">verifies</span><span class="o">();</span>
<span class="k">return</span> <span class="n">Unit</span><span class="o">.</span><span class="na">INSTANCE</span><span class="o">;</span>
<span class="o">});</span>
<span class="o">}</span>
</pre></div>
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