Install debug probes in CoroutinesTimeout constructor to capture coroutines launched from within a test constructor

Fixes #1542

Author: qwwdfsad

kotlinx-coroutines-debug/README.md

@@ -31,8 +31,7 @@ Its usage is better demonstrated by the example (runnable code is [here](test/Te
 
 ```kotlin
 class TestRuleExample {
-    @Rule
-    @JvmField
+    @get:Rule
     public val timeout = CoroutinesTimeout.seconds(1)
 
     private suspend fun someFunctionDeepInTheStack() {

kotlinx-coroutines-debug/src/junit4/CoroutinesTimeout.kt

@@ -21,17 +21,15 @@ import java.util.concurrent.*
  * Example of usage:
  * ```
  * class HangingTest {
+ *     @get:Rule
+ *     val timeout = CoroutinesTimeout.seconds(5)
  *
- *   @Rule
- *   @JvmField
- *   val timeout = CoroutinesTimeout.seconds(5)
- *
- *   @Test
- *   fun testThatHangs() = runBlocking {
- *     ...
- *     delay(Long.MAX_VALUE) // somewhere deep in the stack
- *     ...
- *   }
+ *     @Test
+ *     fun testThatHangs() = runBlocking {
+ *          ...
+ *          delay(Long.MAX_VALUE) // somewhere deep in the stack
+ *          ...
+ *     }
  * }
  * ```
  */
@@ -42,6 +40,11 @@ public class CoroutinesTimeout(
 
     init {
         require(testTimeoutMs > 0) { "Expected positive test timeout, but had $testTimeoutMs" }
+        /*
+         * Install probes in the constructor, so all the coroutines launched from within
+         * target test constructor will be captured
+         */
+        DebugProbes.install()
     }
 
     companion object {

kotlinx-coroutines-debug/src/junit4/CoroutinesTimeoutStatement.kt

@@ -30,11 +30,10 @@ internal class CoroutinesTimeoutStatement(
     private val testThread =  Thread(testResult, "Timeout test thread").apply { isDaemon = true }
 
     override fun evaluate() {
-        DebugProbes.install()
-        testThread.start()
-        // Await until test is started to take only test execution time into account
-        testStartedLatch.await()
         try {
+            testThread.start()
+            // Await until test is started to take only test execution time into account
+            testStartedLatch.await()
             testResult.get(testTimeoutMs, TimeUnit.MILLISECONDS)
             return
         } catch (e: TimeoutException) {

kotlinx-coroutines-debug/test/junit4/CoroutinesTimeoutEagerTest.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.debug.junit4
+
+import kotlinx.coroutines.*
+import org.junit.*
+import org.junit.runners.model.*
+
+class CoroutinesTimeoutEagerTest : TestBase() {
+
+    @Rule
+    @JvmField
+    public val validation = TestFailureValidation(
+        500, true,
+        TestResultSpec(
+            "hangingTest", expectedOutParts = listOf(
+                "Coroutines dump",
+                "Test hangingTest timed out after 500 milliseconds",
+                "BlockingCoroutine{Active}",
+                "runBlocking",
+                "at kotlinx.coroutines.debug.junit4.CoroutinesTimeoutEagerTest.hangForever",
+                "at kotlinx.coroutines.debug.junit4.CoroutinesTimeoutEagerTest.waitForHangJob"),
+            error = TestTimedOutException::class.java)
+    )
+
+    private val job = GlobalScope.launch(Dispatchers.Unconfined) { hangForever() }
+
+    private suspend fun hangForever() {
+        suspendCancellableCoroutine<Unit> {  }
+        expectUnreached()
+    }
+
+    @Test
+    fun hangingTest() = runBlocking<Unit> {
+        waitForHangJob()
+        expectUnreached()
+    }
+
+    private suspend fun waitForHangJob() {
+        job.join()
+        expectUnreached()
+    }
+
+}