diff --git a/contracts/src/test/kotlin/com/r3corda/contracts/CommercialPaperTests.kt b/contracts/src/test/kotlin/com/r3corda/contracts/CommercialPaperTests.kt
index df4cb63a3f..992b76d1a6 100644
--- a/contracts/src/test/kotlin/com/r3corda/contracts/CommercialPaperTests.kt
+++ b/contracts/src/test/kotlin/com/r3corda/contracts/CommercialPaperTests.kt
@@ -85,7 +85,7 @@ class CommercialPaperTestsGeneric {
                 input("paper")
                 input("alice's $900")
                 output("borrowed $900") { 900.DOLLARS.CASH `issued by` issuer `owned by` MEGA_CORP_PUBKEY }
-                output("alice's paper") { "paper".output<ICommercialPaperState>().data `owned by` ALICE_PUBKEY }
+                output("alice's paper") { "paper".output<ICommercialPaperState>() `owned by` ALICE_PUBKEY }
                 command(ALICE_PUBKEY) { Cash.Commands.Move() }
                 command(MEGA_CORP_PUBKEY) { thisTest.getMoveCommand() }
                 this.verifies()
@@ -120,7 +120,7 @@ class CommercialPaperTestsGeneric {
                 timestamp(TEST_TX_TIME + 8.days)
 
                 tweak {
-                    output { "paper".output<ICommercialPaperState>().data }
+                    output { "paper".output<ICommercialPaperState>() }
                     this `fails with` "must be destroyed"
                 }
 
diff --git a/contracts/src/test/kotlin/com/r3corda/contracts/IRSTests.kt b/contracts/src/test/kotlin/com/r3corda/contracts/IRSTests.kt
index e771e25140..ad5e16482f 100644
--- a/contracts/src/test/kotlin/com/r3corda/contracts/IRSTests.kt
+++ b/contracts/src/test/kotlin/com/r3corda/contracts/IRSTests.kt
@@ -377,11 +377,11 @@ class IRSTests {
                 input("irs post agreement")
                 val postAgreement = "irs post agreement".output<InterestRateSwap.State>()
                 output("irs post first fixing") {
-                    postAgreement.data.copy(
-                            postAgreement.data.fixedLeg,
-                            postAgreement.data.floatingLeg,
-                            postAgreement.data.calculation.applyFixing(ld, FixedRate(RatioUnit(bd))),
-                            postAgreement.data.common
+                    postAgreement.copy(
+                            postAgreement.fixedLeg,
+                            postAgreement.floatingLeg,
+                            postAgreement.calculation.applyFixing(ld, FixedRate(RatioUnit(bd))),
+                            postAgreement.common
                     )
                 }
                 command(ORACLE_PUBKEY) {
@@ -693,20 +693,20 @@ class IRSTests {
                 input("irs post agreement2")
                 val postAgreement1 = "irs post agreement1".output<InterestRateSwap.State>()
                 output("irs post first fixing1") {
-                    postAgreement1.data.copy(
-                            postAgreement1.data.fixedLeg,
-                            postAgreement1.data.floatingLeg,
-                            postAgreement1.data.calculation.applyFixing(ld1, FixedRate(RatioUnit(bd1))),
-                            postAgreement1.data.common.copy(tradeID = "t1")
+                    postAgreement1.copy(
+                            postAgreement1.fixedLeg,
+                            postAgreement1.floatingLeg,
+                            postAgreement1.calculation.applyFixing(ld1, FixedRate(RatioUnit(bd1))),
+                            postAgreement1.common.copy(tradeID = "t1")
                     )
                 }
                 val postAgreement2 = "irs post agreement2".output<InterestRateSwap.State>()
                 output("irs post first fixing2") {
-                    postAgreement2.data.copy(
-                            postAgreement2.data.fixedLeg,
-                            postAgreement2.data.floatingLeg,
-                            postAgreement2.data.calculation.applyFixing(ld1, FixedRate(RatioUnit(bd1))),
-                            postAgreement2.data.common.copy(tradeID = "t2")
+                    postAgreement2.copy(
+                            postAgreement2.fixedLeg,
+                            postAgreement2.floatingLeg,
+                            postAgreement2.calculation.applyFixing(ld1, FixedRate(RatioUnit(bd1))),
+                            postAgreement2.common.copy(tradeID = "t2")
                     )
                 }
 
diff --git a/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.java b/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.java
new file mode 100644
index 0000000000..79acf19ae9
--- /dev/null
+++ b/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.java
@@ -0,0 +1,225 @@
+package com.r3corda.contracts.asset;
+
+import kotlin.Unit;
+import org.junit.Test;
+
+import static com.r3corda.core.testing.JavaTestHelpers.*;
+import static com.r3corda.core.contracts.JavaTestHelpers.*;
+
+public class TmpTest {
+
+    public static class Asd {
+        @Test
+        public void emptyLedger() {
+            ledger(l -> {
+                return Unit.INSTANCE;
+            });
+        }
+//
+//        @Test
+//        public void simpleCashDoesntCompile() {
+//            Cash.State inState = new Cash.State(
+//                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+//                    getDUMMY_PUBKEY_1()
+//            );
+//            ledger(l -> {
+//                l.transaction(tx -> {
+//                    tx.input(inState);
+//                });
+//                return Unit.INSTANCE;
+//            });
+//        }
+
+        @Test
+        public void simpleCash() {
+            Cash.State inState = new Cash.State(
+                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                    getDUMMY_PUBKEY_1()
+            );
+            ledger(l -> {
+                l.transaction(tx -> {
+                    tx.input(inState);
+                    return tx.verifies();
+                });
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void simpleCashFailsWith() {
+            Cash.State inState = new Cash.State(
+                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                    getDUMMY_PUBKEY_1()
+            );
+            ledger(l -> {
+                l.transaction(tx -> {
+                    tx.input(inState);
+                    return tx.failsWith("the amounts balance");
+                });
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void simpleCashSuccess() {
+            Cash.State inState = new Cash.State(
+                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                    getDUMMY_PUBKEY_1()
+            );
+            ledger(l -> {
+                l.transaction(tx -> {
+                    tx.input(inState);
+                    tx.failsWith("the amounts balance");
+                    tx.output(inState.copy(inState.getAmount(), getDUMMY_PUBKEY_2()));
+                    tx.command(getDUMMY_PUBKEY_1(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void simpleCashTweakSuccess() {
+            Cash.State inState = new Cash.State(
+                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                    getDUMMY_PUBKEY_1()
+            );
+            ledger(l -> {
+                l.transaction(tx -> {
+                    tx.input(inState);
+                    tx.failsWith("the amounts balance");
+                    tx.output(inState.copy(inState.getAmount(), getDUMMY_PUBKEY_2()));
+
+                    tx.tweak(tw -> {
+                        tw.command(getDUMMY_PUBKEY_2(), new Cash.Commands.Move());
+                        return tw.failsWith("the owning keys are the same as the signing keys");
+                    });
+                    tx.command(getDUMMY_PUBKEY_1(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void simpleCashTweakSuccessTopLevelTransaction() {
+            Cash.State inState = new Cash.State(
+                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                    getDUMMY_PUBKEY_1()
+            );
+            transaction(tx -> {
+                tx.input(inState);
+                tx.failsWith("the amounts balance");
+                tx.output(inState.copy(inState.getAmount(), getDUMMY_PUBKEY_2()));
+
+                tx.tweak(tw -> {
+                    tw.command(getDUMMY_PUBKEY_2(), new Cash.Commands.Move());
+                    return tw.failsWith("the owning keys are the same as the signing keys");
+                });
+                tx.command(getDUMMY_PUBKEY_1(), new Cash.Commands.Move());
+                return tx.verifies();
+            });
+        }
+
+
+        @Test
+        public void chainCash() {
+            ledger(l -> {
+                l.unverifiedTransaction(tx -> {
+                    tx.output("MEGA_CORP cash",
+                            new Cash.State(
+                                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                                    getMEGA_CORP_PUBKEY()
+                            )
+                    );
+                    return Unit.INSTANCE;
+                });
+
+                l.transaction(tx -> {
+                    tx.input("MEGA_CORP cash");
+                    Cash.State inputCash = l.retrieveOutput(Cash.State.class, "MEGA_CORP cash");
+                    tx.output(inputCash.copy(inputCash.getAmount(), getDUMMY_PUBKEY_1()));
+                    tx.command(getMEGA_CORP_PUBKEY(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void chainCashDoubleSpend() {
+            ledger(l -> {
+                l.unverifiedTransaction(tx -> {
+                    tx.output("MEGA_CORP cash",
+                            new Cash.State(
+                                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                                    getMEGA_CORP_PUBKEY()
+                            )
+                    );
+                    return Unit.INSTANCE;
+                });
+
+                l.transaction(tx -> {
+                    tx.input("MEGA_CORP cash");
+                    Cash.State inputCash = l.retrieveOutput(Cash.State.class, "MEGA_CORP cash");
+                    tx.output(inputCash.copy(inputCash.getAmount(), getDUMMY_PUBKEY_1()));
+                    tx.command(getMEGA_CORP_PUBKEY(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+
+                l.transaction(tx -> {
+                    tx.input("MEGA_CORP cash");
+                    Cash.State inputCash = l.retrieveOutput(Cash.State.class, "MEGA_CORP cash");
+                    // We send it to another pubkey so that the transaction is not identical to the previous one
+                    tx.output(inputCash.copy(inputCash.getAmount(), getDUMMY_PUBKEY_2()));
+                    tx.command(getMEGA_CORP_PUBKEY(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+
+                return Unit.INSTANCE;
+            });
+        }
+
+        @Test
+        public void chainCashDoubleSpendFailsWith() {
+            ledger(l -> {
+                l.unverifiedTransaction(tx -> {
+                    tx.output("MEGA_CORP cash",
+                            new Cash.State(
+                                    issuedBy(DOLLARS(1000), getMEGA_CORP().ref((byte)1, (byte)1)),
+                                    getMEGA_CORP_PUBKEY()
+                            )
+                    );
+                    return Unit.INSTANCE;
+                });
+
+                l.transaction(tx -> {
+                    tx.input("MEGA_CORP cash");
+                    Cash.State inputCash = l.retrieveOutput(Cash.State.class, "MEGA_CORP cash");
+                    tx.output(inputCash.copy(inputCash.getAmount(), getDUMMY_PUBKEY_1()));
+                    tx.command(getMEGA_CORP_PUBKEY(), new Cash.Commands.Move());
+                    return tx.verifies();
+                });
+
+                l.tweak(lw -> {
+                    lw.transaction(tx -> {
+                        tx.input("MEGA_CORP cash");
+                        Cash.State inputCash = l.retrieveOutput(Cash.State.class, "MEGA_CORP cash");
+                        // We send it to another pubkey so that the transaction is not identical to the previous one
+                        tx.output(inputCash.copy(inputCash.getAmount(), getDUMMY_PUBKEY_2()));
+                        tx.command(getMEGA_CORP_PUBKEY(), new Cash.Commands.Move());
+                        return tx.verifies();
+                    });
+                    lw.fails();
+                    return Unit.INSTANCE;
+                });
+
+                l.verifies();
+                return Unit.INSTANCE;
+            });
+        }
+
+
+    }
+}
diff --git a/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.kt b/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.kt
new file mode 100644
index 0000000000..e77b341846
--- /dev/null
+++ b/contracts/src/test/kotlin/com/r3corda/contracts/asset/TmpTest.kt
@@ -0,0 +1,209 @@
+package com.r3corda.contracts.asset
+
+import com.r3corda.core.contracts.DOLLARS
+import com.r3corda.core.contracts.`issued by`
+import com.r3corda.core.testing.*
+import org.junit.Test
+
+
+class Asd {
+
+    class Asd {
+
+        @Test
+        fun emptyLedger() {
+            ledger {
+            }
+        }
+//
+//        @Test
+//        fun simpleCashFails() {
+//            ledger {
+//                transaction {
+//                    input(Cash.State(
+//                            amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+//                            owner = DUMMY_PUBKEY_1
+//                    ))
+//                    this.verifies()
+//                }
+//            }
+//        }
+
+        @Test
+        fun simpleCash() {
+            val inState = Cash.State(
+                    amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                    owner = DUMMY_PUBKEY_1
+            )
+            ledger {
+                transaction {
+                    input(inState)
+                    this.verifies()
+                }
+            }
+        }
+
+        @Test
+        fun simpleCashFailsWith() {
+            val inState = Cash.State(
+                    amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                    owner = DUMMY_PUBKEY_1
+            )
+            ledger {
+                transaction {
+                    input(inState)
+                    this `fails with` "the amounts balance"
+                }
+            }
+        }
+
+        @Test
+        fun simpleCashSuccess() {
+            val inState = Cash.State(
+                    amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                    owner = DUMMY_PUBKEY_1
+            )
+            ledger {
+                transaction {
+                    input(inState)
+                    this `fails with` "the amounts balance"
+                    output(inState.copy(owner = DUMMY_PUBKEY_2))
+                    command(DUMMY_PUBKEY_1) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+            }
+        }
+
+        @Test
+        fun simpleCashTweakSuccess() {
+            val inState = Cash.State(
+                    amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                    owner = DUMMY_PUBKEY_1
+            )
+            ledger {
+                transaction {
+                    input(inState)
+                    this `fails with` "the amounts balance"
+                    output(inState.copy(owner = DUMMY_PUBKEY_2))
+
+                    tweak {
+                        command(DUMMY_PUBKEY_2) { Cash.Commands.Move() }
+                        this `fails with` "the owning keys are the same as the signing keys"
+                    }
+
+                    command(DUMMY_PUBKEY_1) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+            }
+        }
+
+        @Test
+        fun simpleCashTweakSuccessTopLevelTransaction() {
+            val inState = Cash.State(
+                    amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                    owner = DUMMY_PUBKEY_1
+            )
+            transaction {
+                input(inState)
+                this `fails with` "the amounts balance"
+                output(inState.copy(owner = DUMMY_PUBKEY_2))
+
+                tweak {
+                    command(DUMMY_PUBKEY_2) { Cash.Commands.Move() }
+                    this `fails with` "the owning keys are the same as the signing keys"
+                }
+
+                command(DUMMY_PUBKEY_1) { Cash.Commands.Move() }
+                this.verifies()
+            }
+        }
+
+
+        @Test
+        fun chainCash() {
+            ledger {
+                unverifiedTransaction {
+                    output("MEGA_CORP cash") {
+                        Cash.State(
+                                amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                                owner = MEGA_CORP_PUBKEY
+                        )
+                    }
+                }
+
+                transaction {
+                    input("MEGA_CORP cash")
+                    output("MEGA_CORP cash".output<Cash.State>().copy(owner = DUMMY_PUBKEY_1))
+                    command(MEGA_CORP_PUBKEY) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+            }
+        }
+
+
+        @Test
+        fun chainCashDoubleSpend() {
+            ledger {
+                unverifiedTransaction {
+                    output("MEGA_CORP cash") {
+                        Cash.State(
+                                amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                                owner = MEGA_CORP_PUBKEY
+                        )
+                    }
+                }
+
+                transaction {
+                    input("MEGA_CORP cash")
+                    output("MEGA_CORP cash".output<Cash.State>().copy(owner = DUMMY_PUBKEY_1))
+                    command(MEGA_CORP_PUBKEY) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+
+                transaction {
+                    input("MEGA_CORP cash")
+                    // We send it to another pubkey so that the transaction is not identical to the previous one
+                    output("MEGA_CORP cash".output<Cash.State>().copy(owner = DUMMY_PUBKEY_1))
+                    command(MEGA_CORP_PUBKEY) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+            }
+        }
+
+        @Test
+        fun chainCashDoubleSpendFailsWith() {
+            ledger {
+                unverifiedTransaction {
+                    output("MEGA_CORP cash") {
+                        Cash.State(
+                                amount = 1000.DOLLARS `issued by` MEGA_CORP.ref(1, 1),
+                                owner = MEGA_CORP_PUBKEY
+                        )
+                    }
+                }
+
+                transaction {
+                    input("MEGA_CORP cash")
+                    output("MEGA_CORP cash".output<Cash.State>().copy(owner = DUMMY_PUBKEY_1))
+                    command(MEGA_CORP_PUBKEY) { Cash.Commands.Move() }
+                    this.verifies()
+                }
+
+                tweak {
+                    transaction {
+                        input("MEGA_CORP cash")
+                        // We send it to another pubkey so that the transaction is not identical to the previous one
+                        output("MEGA_CORP cash".output<Cash.State>().copy(owner = DUMMY_PUBKEY_2))
+                        command(MEGA_CORP_PUBKEY) { Cash.Commands.Move() }
+                        this.verifies()
+                    }
+                    this.fails()
+                }
+
+                this.verifies()
+            }
+        }
+    }
+
+}
+
diff --git a/core/src/main/kotlin/com/r3corda/core/crypto/CryptoUtilities.kt b/core/src/main/kotlin/com/r3corda/core/crypto/CryptoUtilities.kt
index 70c99809a5..60c1417dd3 100644
--- a/core/src/main/kotlin/com/r3corda/core/crypto/CryptoUtilities.kt
+++ b/core/src/main/kotlin/com/r3corda/core/crypto/CryptoUtilities.kt
@@ -169,4 +169,4 @@ operator fun KeyPair.component1() = this.private
 operator fun KeyPair.component2() = this.public
 
 /** A simple wrapper that will make it easier to swap out the EC algorithm we use in future */
-fun generateKeyPair() = EddsaKeyPairGenerator().generateKeyPair()!!
+fun generateKeyPair(): KeyPair = EddsaKeyPairGenerator().generateKeyPair()
diff --git a/core/src/main/kotlin/com/r3corda/core/testing/LedgerDSLInterpreter.kt b/core/src/main/kotlin/com/r3corda/core/testing/LedgerDSLInterpreter.kt
index 92b18fe99c..c80aa84a9d 100644
--- a/core/src/main/kotlin/com/r3corda/core/testing/LedgerDSLInterpreter.kt
+++ b/core/src/main/kotlin/com/r3corda/core/testing/LedgerDSLInterpreter.kt
@@ -61,6 +61,12 @@ interface LedgerDSLInterpreter<R, out T : TransactionDSLInterpreter<R>> : Output
      * Verifies the ledger using [TransactionGroup.verify], throws if the verification fails.
      */
     fun verifies()
+
+    /**
+     * Verifies the ledger, expecting an exception to be thrown.
+     * @param expectedMessage: An optional string to be searched for in the raised exception.
+     */
+    fun failsWith(expectedMessage: String?)
 }
 
 /**
@@ -97,12 +103,28 @@ class LedgerDSL<R, out T : TransactionDSLInterpreter<R>, out L : LedgerDSLInterp
      * Retrieves the output [TransactionState] based on the label.
      * @see OutputStateLookup.retrieveOutputStateAndRef
      */
-    inline fun <reified S : ContractState> String.output(): TransactionState<S> =
-            outputStateAndRef<S>().state
+    inline fun <reified S : ContractState> String.output(): S =
+            outputStateAndRef<S>().state.data
 
     /**
      * Retrieves the output [StateRef] based on the label.
      * @see OutputStateLookup.retrieveOutputStateAndRef
      */
     fun String.outputRef(): StateRef = outputStateAndRef<ContractState>().ref
+
+    /**
+     * @see OutputStateLookup.retrieveOutputStateAndRef
+     */
+    fun <S : ContractState> retrieveOutput(clazz: Class<S>, label: String) =
+            retrieveOutputStateAndRef(clazz, label).state.data
+
+    /**
+     * Asserts that the transaction will fail verification
+     */
+    fun fails() = failsWith(null)
+
+    /**
+     * @see TransactionDSLInterpreter.failsWith
+     */
+    infix fun `fails with`(msg: String) = failsWith(msg)
 }
diff --git a/core/src/main/kotlin/com/r3corda/core/testing/TestDSL.kt b/core/src/main/kotlin/com/r3corda/core/testing/TestDSL.kt
index 5b26a17698..8a820c18a0 100644
--- a/core/src/main/kotlin/com/r3corda/core/testing/TestDSL.kt
+++ b/core/src/main/kotlin/com/r3corda/core/testing/TestDSL.kt
@@ -161,27 +161,8 @@ data class TestTransactionDSLInterpreter private constructor(
     }
 
     override fun failsWith(expectedMessage: String?): EnforceVerifyOrFail {
-        val exceptionThrown = try {
+        expectExceptionContainingString(expectedMessage) {
             this.verifies()
-            false
-        } catch (exception: Exception) {
-            if (expectedMessage != null) {
-                val exceptionMessage = exception.message
-                if (exceptionMessage == null) {
-                    throw AssertionError(
-                            "Expected exception containing '$expectedMessage' but raised exception had no message"
-                    )
-                } else if (!exceptionMessage.toLowerCase().contains(expectedMessage.toLowerCase())) {
-                    throw AssertionError(
-                            "Expected exception containing '$expectedMessage' but raised exception was '$exception'"
-                    )
-                }
-            }
-            true
-        }
-
-        if (!exceptionThrown) {
-            throw AssertionError("Expected exception but didn't get one")
         }
 
         return EnforceVerifyOrFail.Token
@@ -202,7 +183,6 @@ data class TestLedgerDSLInterpreter private constructor (
         private val transactionWithLocations: HashMap<SecureHash, WireTransactionWithLocation> = HashMap(),
         private val nonVerifiedTransactionWithLocations: HashMap<SecureHash, WireTransactionWithLocation> = HashMap()
 ) : LedgerDSLInterpreter<EnforceVerifyOrFail, TestTransactionDSLInterpreter> {
-
     val wireTransactions: List<WireTransaction> get() = transactionWithLocations.values.map { it.transaction }
 
     // We specify [labelToOutputStateAndRefs] just so that Kotlin picks the primary constructor instead of cycling
@@ -211,19 +191,25 @@ data class TestLedgerDSLInterpreter private constructor (
     )
 
     companion object {
-        private fun getCallerLocation(offset: Int): String {
-            val stackTraceElement = Thread.currentThread().stackTrace[3 + offset]
-            return stackTraceElement.toString()
+        private fun getCallerLocation(): String? {
+            val stackTrace = Thread.currentThread().stackTrace
+            for (i in 1 .. stackTrace.size) {
+                val stackTraceElement = stackTrace[i]
+                if (!stackTraceElement.fileName.contains("DSL")) {
+                    return stackTraceElement.toString()
+                }
+            }
+            return null
         }
     }
 
     internal data class WireTransactionWithLocation(
             val label: String?,
             val transaction: WireTransaction,
-            val location: String
+            val location: String?
     )
-    class VerifiesFailed(transactionLocation: String, cause: Throwable) :
-            Exception("Transaction defined at ($transactionLocation) didn't verify: $cause", cause)
+    class VerifiesFailed(transactionName: String, cause: Throwable) :
+            Exception("Transaction ($transactionName) didn't verify: $cause", cause)
     class TypeMismatch(requested: Class<*>, actual: Class<*>) :
             Exception("Actual type $actual is not a subtype of requested type $requested")
 
@@ -309,7 +295,7 @@ data class TestLedgerDSLInterpreter private constructor (
             dsl: TransactionDSL<EnforceVerifyOrFail, TestTransactionDSLInterpreter>.() -> R,
             transactionMap: HashMap<SecureHash, WireTransactionWithLocation> = HashMap()
     ): WireTransaction {
-        val transactionLocation = getCallerLocation(3)
+        val transactionLocation = getCallerLocation()
         val transactionInterpreter = interpretTransactionDsl(transactionBuilder, dsl)
         // Create the WireTransaction
         val wireTransaction = transactionInterpreter.toWireTransaction()
@@ -353,7 +339,15 @@ data class TestLedgerDSLInterpreter private constructor (
         try {
             transactionGroup.verify()
         } catch (exception: TransactionVerificationException) {
-            throw VerifiesFailed(transactionWithLocations[exception.tx.origHash]?.location ?: "<unknown>", exception)
+            val transactionWithLocation = transactionWithLocations[exception.tx.origHash]
+            val transactionName = transactionWithLocation?.label ?: transactionWithLocation?.location ?: "<unknown>"
+            throw VerifiesFailed(transactionName, exception)
+        }
+    }
+
+    override fun failsWith(expectedMessage: String?) {
+        expectExceptionContainingString(expectedMessage) {
+            this.verifies()
         }
     }
 
@@ -397,3 +391,28 @@ fun signAll(transactionsToSign: List<WireTransaction>, extraKeys: Array<out KeyP
  */
 fun LedgerDSL<EnforceVerifyOrFail, TestTransactionDSLInterpreter, TestLedgerDSLInterpreter>.signAll(
         vararg extraKeys: KeyPair) = signAll(this.interpreter.wireTransactions, extraKeys)
+
+internal inline fun expectExceptionContainingString(string: String?, body:() -> Unit) {
+    val exceptionThrown = try {
+        body()
+        false
+    } catch (exception: Exception) {
+        if (string != null) {
+            val exceptionMessage = exception.message
+            if (exceptionMessage == null) {
+                throw AssertionError(
+                        "Expected exception containing '$string' but raised exception had no message"
+                )
+            } else if (!exceptionMessage.toLowerCase().contains(string.toLowerCase())) {
+                throw AssertionError(
+                        "Expected exception containing '$string' but raised exception was '$exception'"
+                )
+            }
+        }
+        true
+    }
+
+    if (!exceptionThrown) {
+        throw AssertionError("Expected exception but didn't get one")
+    }
+}
diff --git a/core/src/main/kotlin/com/r3corda/core/testing/TransactionDSLInterpreter.kt b/core/src/main/kotlin/com/r3corda/core/testing/TransactionDSLInterpreter.kt
index 6b93ec3294..2816d77990 100644
--- a/core/src/main/kotlin/com/r3corda/core/testing/TransactionDSLInterpreter.kt
+++ b/core/src/main/kotlin/com/r3corda/core/testing/TransactionDSLInterpreter.kt
@@ -96,10 +96,12 @@ class TransactionDSL<R, out T : TransactionDSLInterpreter<R>> (val interpreter:
     /**
      * @see TransactionDSLInterpreter._output
      */
-    @JvmOverloads
-    fun output(label: String? = null, contractState: ContractState) =
+    fun output(label: String, contractState: ContractState) =
             _output(label, DUMMY_NOTARY, contractState)
 
+    fun output(contractState: ContractState) =
+            _output(null, DUMMY_NOTARY, contractState)
+
     /**
      * @see TransactionDSLInterpreter._command
      */
diff --git a/node/src/main/kotlin/com/r3corda/node/internal/testing/MockNode.kt b/node/src/main/kotlin/com/r3corda/node/internal/testing/MockNode.kt
index 6245192984..cdb5699b91 100644
--- a/node/src/main/kotlin/com/r3corda/node/internal/testing/MockNode.kt
+++ b/node/src/main/kotlin/com/r3corda/node/internal/testing/MockNode.kt
@@ -88,7 +88,7 @@ class MockNetwork(private val networkSendManuallyPumped: Boolean = false,
             // Nothing to do
         }
 
-        override fun generateKeyPair(): KeyPair? = keyPair ?: super.generateKeyPair()
+        override fun generateKeyPair(): KeyPair = keyPair ?: super.generateKeyPair()
 
         // It's OK to not have a network map service in the mock network.
         override fun noNetworkMapConfigured() = Futures.immediateFuture(Unit)