CORDA-1862: Allow MockNetwork to create StartedMockNode from UnstartedMockNode. (#3731)

* Allow MockNetwork to create StartedMockNode from UnstartedMockNode.
* Reimplement by adding a `started` property to UnstartedMockNode.
* Throw IllegalStateException instead of NoSuchElementException.
* Add an isStarted property to UnstartedMockNode.

testing/node-driver/src/main/kotlin/net/corda/testing/node/MockNetwork.kt

@@ -128,6 +128,18 @@ class UnstartedMockNode private constructor(private val node: InternalMockNetwor
      * @return A [StartedMockNode] object.
      */
     fun start(): StartedMockNode = StartedMockNode.create(node.start())
+
+    /**
+     * A [StartedMockNode] object for this running node.
+     * @throws [IllegalStateException] if the node is not running yet.
+     */
+    val started: StartedMockNode
+        get() = StartedMockNode.create(node.started ?: throw IllegalStateException("Node ID=$id is not running"))
+
+    /**
+     * Whether this node has been started yet.
+     */
+    val isStarted: Boolean get() = node.started != null
 }
 
 /** A class that represents a started mock node for testing. */

testing/node-driver/src/test/kotlin/net/corda/testing/node/MockNetworkTest.kt

@@ -0,0 +1,47 @@
+package net.corda.testing.node
+
+import net.corda.testing.core.*
+import org.assertj.core.api.Assertions.*
+import org.junit.After
+import org.junit.Assert.*
+import org.junit.Before
+import org.junit.Test
+import kotlin.test.assertFailsWith
+
+class MockNetworkTest {
+    private companion object {
+        private const val NODE_ID = 101
+    }
+    private lateinit var mockNetwork: MockNetwork
+
+    @Before
+    fun setup() {
+        mockNetwork = MockNetwork(cordappPackages = emptyList())
+    }
+
+    @After
+    fun done() {
+        mockNetwork.stopNodes()
+    }
+
+    @Test
+    fun `with a started node`() {
+        val unstarted = mockNetwork.createUnstartedNode(DUMMY_BANK_A_NAME, forcedID = NODE_ID)
+        assertFalse(unstarted.isStarted)
+
+        mockNetwork.startNodes()
+        assertTrue(unstarted.isStarted)
+
+        val started = unstarted.started
+        assertEquals(NODE_ID, started.id)
+        assertEquals(DUMMY_BANK_A_NAME, started.info.identityFromX500Name(DUMMY_BANK_A_NAME).name)
+        assertFailsWith<IllegalArgumentException> { started.info.identityFromX500Name(DUMMY_BANK_B_NAME) }
+    }
+
+    @Test
+    fun `with an unstarted node`() {
+        val unstarted = mockNetwork.createUnstartedNode(DUMMY_BANK_A_NAME, forcedID = NODE_ID)
+        val ex = assertFailsWith<IllegalStateException> { unstarted.started }
+        assertThat(ex).hasMessage("Node ID=$NODE_ID is not running")
+    }
+}