Adding a test-helper class TestCoroutineContext.

Author: Anton Spaans

core/kotlinx-coroutines-core/README.md

@@ -69,6 +69,10 @@ This module provides debugging facilities for coroutines (run JVM with `-ea` or
 and [newCoroutineContext] function to write user-defined coroutine builders that work with these
 debugging facilities.
 
+This module provides a special CoroutineContext type [TestCoroutineCoroutineContext][kotlinx.coroutines.experimental.test.TestCoroutineContext] that
+allows the writer of code that contains Coroutines with delays and timeouts to write non-flaky unit-tests for that code allowing these tests to
+terminate in near zero time. See the documentation for this class for more information.
+
 # Package kotlinx.coroutines.experimental
 
 General-purpose coroutine builders, contexts, and helper functions.
@@ -93,6 +97,10 @@ Low-level primitives for finer-grained control of coroutines.
 
 Optional time unit support for multiplatform projects.
 
+# Package kotlinx.coroutines.experimental.test
+
+Components to ease writing unit-tests for code that contains coroutines with delays and timeouts.
+
 <!--- MODULE kotlinx-coroutines-core -->
 <!--- INDEX kotlinx.coroutines.experimental -->
 [launch]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental/launch.html
@@ -148,4 +156,6 @@ Optional time unit support for multiplatform projects.
 <!--- INDEX kotlinx.coroutines.experimental.selects -->
 [kotlinx.coroutines.experimental.selects.select]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental.selects/select.html
 [kotlinx.coroutines.experimental.selects.SelectBuilder.onTimeout]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental.selects/-select-builder/on-timeout.html
+<!--- INDEX kotlinx.coroutines.experimental.test -->
+[kotlinx.coroutines.experimental.test.TestCoroutineContext]: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental.test/-test-coroutine-context/index.html
 <!--- END -->

core/kotlinx-coroutines-core/src/main/kotlin/kotlinx/coroutines/experimental/internal/ThreadSafeHeap.kt

@@ -16,6 +16,8 @@
 
 package kotlinx.coroutines.experimental.internal
 
+import java.util.*
+
 /**
  * @suppress **This is unstable API and it is subject to change.**
  */
@@ -36,6 +38,11 @@ public class ThreadSafeHeap<T> where T: ThreadSafeHeapNode, T: Comparable<T> {
 
     public val isEmpty: Boolean get() = size == 0
 
+    public fun clear() = synchronized(this) {
+        Arrays.fill(a, 0, size, null)
+        size = 0
+    }
+
     public fun peek(): T? = synchronized(this) { firstImpl() }
 
     public fun removeFirstOrNull(): T? = synchronized(this) {

core/kotlinx-coroutines-core/src/main/kotlin/kotlinx/coroutines/experimental/test/TestCoroutineContext.kt

@@ -0,0 +1,285 @@
+/*
+ * Copyright 2016-2018 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlinx.coroutines.experimental.test
+
+import kotlinx.coroutines.experimental.*
+import kotlinx.coroutines.experimental.internal.*
+import java.util.concurrent.TimeUnit
+import kotlin.coroutines.experimental.*
+
+/**
+ * This [CoroutineContext] dispatcher can be used to simulate virtual time to speed up
+ * code, especially tests, that deal with delays and timeouts in Coroutines.
+ *
+ * Provide an instance of this TestCoroutineContext when calling the *non-blocking* [launch] or [async]
+ * and then advance time or trigger the actions to make the co-routines execute as soon as possible.
+ *
+ * This works much like the *TestScheduler* in RxJava2, which allows to speed up tests that deal
+ * with non-blocking Rx chains that contain delays, timeouts, intervals and such.
+ *
+ * This dispatcher can also handle *blocking* coroutines that are started by [runBlocking].
+ * This dispatcher's virtual time will be automatically advanced based based on the delayed actions
+ * within the Coroutine(s).
+ *
+ * @param name A user-readable name for debugging purposes.
+ */
+class TestCoroutineContext(private val name: String? = null) : CoroutineContext {
+    private val uncaughtExceptions = mutableListOf<Throwable>()
+
+    private val ctxDispatcher = Dispatcher()
+
+    private val ctxHandler = CoroutineExceptionHandler { _, exception ->
+        uncaughtExceptions += exception
+    }
+
+    // The ordered queue for the runnable tasks.
+    private val queue = ThreadSafeHeap<TimedRunnable>()
+
+    // The per-scheduler global order counter.
+    private var counter = 0L
+
+    // Storing time in nanoseconds internally.
+    private var time = 0L
+
+    /**
+     * Exceptions that were caught during a [launch] or a [async] + [Deferred.await].
+     */
+    public val exceptions: List<Throwable> get() = uncaughtExceptions
+
+    // -- CoroutineContext implementation 
+
+    public override fun <R> fold(initial: R, operation: (R, CoroutineContext.Element) -> R): R =
+        operation(operation(initial, ctxDispatcher), ctxHandler)
+
+    @Suppress("UNCHECKED_CAST")
+    public override fun <E : CoroutineContext.Element> get(key: CoroutineContext.Key<E>): E? = when {
+        key === ContinuationInterceptor -> ctxDispatcher as E
+        key === CoroutineExceptionHandler -> ctxHandler as E
+        else -> null
+    }
+
+    public override fun minusKey(key: CoroutineContext.Key<*>): CoroutineContext = when {
+        key === ContinuationInterceptor -> ctxHandler
+        key === CoroutineExceptionHandler -> ctxDispatcher
+        else -> this
+    }
+
+    /**
+     * Returns the current virtual clock-time as it is known to this CoroutineContext.
+     *
+     * @param unit The [TimeUnit] in which the clock-time must be returned.
+     * @return The virtual clock-time
+     */
+    public fun now(unit: TimeUnit = TimeUnit.MILLISECONDS)=
+        unit.convert(time, TimeUnit.NANOSECONDS)
+
+    /**
+     * Moves the CoroutineContext's virtual clock forward by a specified amount of time.
+     *
+     * The returned delay-time can be larger than the specified delay-time if the code
+     * under test contains *blocking* Coroutines.
+     *
+     * @param delayTime The amount of time to move the CoroutineContext's clock forward.
+     * @param unit The [TimeUnit] in which [delayTime] and the return value is expressed.
+     * @return The amount of delay-time that this CoroutinesContext's clock has been forwarded.
+     */
+    public fun advanceTimeBy(delayTime: Long, unit: TimeUnit = TimeUnit.MILLISECONDS): Long {
+        val oldTime = time
+        advanceTimeTo(oldTime + unit.toNanos(delayTime), TimeUnit.NANOSECONDS)
+        return unit.convert(time - oldTime, TimeUnit.NANOSECONDS)
+    }
+
+    /**
+     * Moves the CoroutineContext's clock-time to a particular moment in time.
+     *
+     * @param targetTime The point in time to which to move the CoroutineContext's clock.
+     * @param unit The [TimeUnit] in which [targetTime] is expressed.
+     */
+    fun advanceTimeTo(targetTime: Long, unit: TimeUnit = TimeUnit.MILLISECONDS) {
+        val nanoTime = unit.toNanos(targetTime)
+        triggerActions(nanoTime)
+        if (nanoTime > time) time = nanoTime
+    }
+
+    /**
+     * Triggers any actions that have not yet been triggered and that are scheduled to be triggered at or
+     * before this CoroutineContext's present virtual clock-time.
+     */
+    public fun triggerActions() = triggerActions(time)
+
+    /**
+     * Cancels all not yet triggered actions. Be careful calling this, since it can seriously
+     * mess with your coroutines work. This method should usually be called on tear-down of a
+     * unit test.
+     */
+    public fun cancelAllActions() {
+        // An 'is-empty' test is required to avoid a NullPointerException in the 'clear()' method
+        if (!queue.isEmpty) queue.clear()
+    }
+
+    /**
+     * This method does nothing if there is one unhandled exception that satisfies the given predicate.
+     * Otherwise it throws an [AssertionError] with the given message.
+     *
+     * (this method will clear the list of unhandled exceptions)
+     *
+     * @param message Message of the [AssertionError]. Defaults to an empty String.
+     * @param predicate The predicate that must be satisfied.
+     */
+    public fun assertUnhandledException(message: String = "", predicate: (Throwable) -> Boolean) {
+        if (uncaughtExceptions.size != 1 || !predicate(uncaughtExceptions[0])) throw AssertionError(message)
+        uncaughtExceptions.clear()
+    }
+
+    /**
+     * This method does nothing if there are no unhandled exceptions or all of them satisfy the given predicate.
+     * Otherwise it throws an [AssertionError] with the given message.
+     *
+     * (this method will clear the list of unhandled exceptions)
+     *
+     * @param message Message of the [AssertionError]. Defaults to an empty String.
+     * @param predicate The predicate that must be satisfied.
+     */
+    public fun assertAllUnhandledExceptions(message: String = "", predicate: (Throwable) -> Boolean) {
+        if (!uncaughtExceptions.all(predicate)) throw AssertionError(message)
+        uncaughtExceptions.clear()
+    }
+
+    /**
+     * This method does nothing if one or more unhandled exceptions satisfy the given predicate.
+     * Otherwise it throws an [AssertionError] with the given message.
+     *
+     * (this method will clear the list of unhandled exceptions)
+     *
+     * @param message Message of the [AssertionError]. Defaults to an empty String.
+     * @param predicate The predicate that must be satisfied.
+     */
+    public fun assertAnyUnhandledException(message: String = "", predicate: (Throwable) -> Boolean) {
+        if (!uncaughtExceptions.any(predicate)) throw AssertionError(message)
+        uncaughtExceptions.clear()
+    }
+
+    /**
+     * This method does nothing if the list of unhandled exceptions satisfy the given predicate.
+     * Otherwise it throws an [AssertionError] with the given message.
+     *
+     * (this method will clear the list of unhandled exceptions)
+     *
+     * @param message Message of the [AssertionError]. Defaults to an empty String.
+     * @param predicate The predicate that must be satisfied.
+     */
+    public fun assertExceptions(message: String = "", predicate: (List<Throwable>) -> Boolean) {
+        if (!predicate(uncaughtExceptions)) throw AssertionError(message)
+        uncaughtExceptions.clear()
+    }
+
+    private fun post(block: Runnable) =
+        queue.addLast(TimedRunnable(block, counter++))
+
+    private fun postDelayed(block: Runnable, delayTime: Long) =
+        TimedRunnable(block, counter++, time + TimeUnit.MILLISECONDS.toNanos(delayTime))
+            .also {
+                queue.addLast(it)
+            }
+
+    private fun processNextEvent(): Long {
+        val current = queue.peek()
+        if (current != null) {
+            /** Automatically advance time for [EventLoop]-callbacks */
+            triggerActions(current.time)
+        }
+        return if (queue.isEmpty) Long.MAX_VALUE else 0L
+    }
+
+    private fun triggerActions(targetTime: Long) {
+        while (true) {
+            val current = queue.removeFirstIf { it.time <= targetTime } ?: break
+            // If the scheduled time is 0 (immediate) use current virtual time
+            if (current.time != 0L) time = current.time
+            current.run()
+        }
+    }
+
+    public override fun toString(): String = name ?: "TestCoroutineContext@$hexAddress"
+
+    private inner class Dispatcher : CoroutineDispatcher(), Delay, EventLoop {
+        override fun dispatch(context: CoroutineContext, block: Runnable) = post(block)
+
+        override fun scheduleResumeAfterDelay(time: Long, unit: TimeUnit, continuation: CancellableContinuation<Unit>) {
+            postDelayed(Runnable {
+                with(continuation) { resumeUndispatched(Unit) }
+            }, unit.toMillis(time))
+        }
+
+        override fun invokeOnTimeout(time: Long, unit: TimeUnit, block: Runnable): DisposableHandle {
+            val node = postDelayed(block, unit.toMillis(time))
+            return object : DisposableHandle {
+                override fun dispose() {
+                    queue.remove(node)
+                }
+            }
+        }
+
+        override fun processNextEvent() = this@TestCoroutineContext.processNextEvent()
+
+        public override fun toString(): String = "Dispatcher(${this@TestCoroutineContext})"
+    }
+}
+
+private class TimedRunnable(
+    private val run: Runnable,
+    private val count: Long = 0,
+    @JvmField internal val time: Long = 0
+) : Comparable<TimedRunnable>, Runnable by run, ThreadSafeHeapNode {
+    override var index: Int = 0
+
+    override fun run() = run.run()
+
+    override fun compareTo(other: TimedRunnable) = if (time == other.time) {
+        count.compareTo(other.count)
+    } else {
+        time.compareTo(other.time)
+    }
+
+    override fun toString() = "TimedRunnable(time=$time, run=$run)"
+}
+
+/**
+ * Executes a block of code in which a unit-test can be written using the provided [TestCoroutineContext]. The provided
+ * [TestCoroutineContext] is available in the [testBody] as the `this` receiver.
+ *
+ * The [testBody] is executed and an [AssertionError] is thrown if the list of unhandled exceptions is not empty and
+ * contains any exception that is not a [CancellationException].
+ *
+ * If the [testBody] successfully executes one of the [TestCoroutineContext.assertAllUnhandledExceptions],
+ * [TestCoroutineContext.assertAnyUnhandledException], [TestCoroutineContext.assertUnhandledException] or
+ * [TestCoroutineContext.assertExceptions], the list of unhandled exceptions will have been cleared and this method will
+ * not throw an [AssertionError].
+ *
+ * @param testContext The provided [TestCoroutineContext]. If not specified, a default [TestCoroutineContext] will be
+ * provided instead.
+ * @param testBody The code of the unit-test.
+ */
+public fun withTestContext(testContext: TestCoroutineContext = TestCoroutineContext(), testBody: TestCoroutineContext.() -> Unit) {
+    with (testContext) {
+        testBody()
+
+        if (!exceptions.all { it is CancellationException }) {
+            throw AssertionError("Coroutine encountered unhandled exceptions:\n${exceptions}")
+        }
+    }
+}