Support disabling reporting of uncaught exceptions in tests (#3736)

The solution for #1205 may be undesirable for those who already
have their own solution, like setting the default exception
handlers. In this case, there's a usability issue without the
corresponding benefit: instead of all tests being ran and the
exceptions from them being reported, unrelated tests may fail,
making looking for problems more difficult.

This is probably a very rare issue, so we don't provide public API
for that, instead introducing a need-to-know internal variable.

kotlinx-coroutines-test/api/kotlinx-coroutines-test.api

@@ -121,9 +121,11 @@ public final class kotlinx/coroutines/test/TestScopeKt {
 	public static final fun advanceTimeBy (Lkotlinx/coroutines/test/TestScope;J)V
 	public static final fun advanceTimeBy-HG0u8IE (Lkotlinx/coroutines/test/TestScope;J)V
 	public static final fun advanceUntilIdle (Lkotlinx/coroutines/test/TestScope;)V
+	public static final fun getCatchNonTestRelatedExceptions ()Z
 	public static final fun getCurrentTime (Lkotlinx/coroutines/test/TestScope;)J
 	public static final fun getTestTimeSource (Lkotlinx/coroutines/test/TestScope;)Lkotlin/time/TimeSource$WithComparableMarks;
 	public static final fun runCurrent (Lkotlinx/coroutines/test/TestScope;)V
+	public static final fun setCatchNonTestRelatedExceptions (Z)V
 }
 
 public abstract interface class kotlinx/coroutines/test/UncaughtExceptionCaptor {

kotlinx-coroutines-test/common/src/TestScope.kt

@@ -233,7 +233,9 @@ internal class TestScopeImpl(context: CoroutineContext) :
              * after the previous one, and learning about such exceptions as soon is possible is nice. */
             @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER")
             run { ensurePlatformExceptionHandlerLoaded(ExceptionCollector) }
-            ExceptionCollector.addOnExceptionCallback(lock, this::reportException)
+            if (catchNonTestRelatedExceptions) {
+                ExceptionCollector.addOnExceptionCallback(lock, this::reportException)
+            }
             uncaughtExceptions
         }
         if (exceptions.isNotEmpty()) {
@@ -321,3 +323,12 @@ internal class UncaughtExceptionsBeforeTest : IllegalStateException(
  */
 @ExperimentalCoroutinesApi
 internal class UncompletedCoroutinesError(message: String) : AssertionError(message)
+
+/**
+ * A flag that controls whether [TestScope] should attempt to catch arbitrary exceptions flying through the system.
+ * If it is enabled, then any exception that is not caught by the user code will be reported as a test failure.
+ * By default, it is enabled, but some tests may want to disable it to test the behavior of the system when they have
+ * their own exception handling procedures.
+ */
+@PublishedApi
+internal var catchNonTestRelatedExceptions: Boolean = true

kotlinx-coroutines-test/common/src/internal/ExceptionCollector.kt

@@ -43,8 +43,10 @@ internal object ExceptionCollector : AbstractCoroutineContextElement(CoroutineEx
      * Unregisters the callback associated with [owner].
      */
     fun removeOnExceptionCallback(owner: Any) = synchronized(lock) {
-        val existingValue = callbacks.remove(owner)
-        check(existingValue !== null)
+        if (enabled) {
+            val existingValue = callbacks.remove(owner)
+            check(existingValue !== null)
+        }
     }
 
     /**