Introduce TestResult into TestBase as the first preparation step to m…

kotlinx-coroutines-core/common/test/TestBase.common.kt

@@ -13,6 +13,13 @@ import kotlin.test.*
 public expect val isStressTest: Boolean
 public expect val stressTestMultiplier: Int
 
+/**
+ * The result of a multiplatform asynchronous test.
+ * Aliases into Unit on K/JVM and K/N, and into Promise on K/JS.
+ */
+@Suppress("NO_ACTUAL_FOR_EXPECT")
+public expect class TestResult
+
 public expect open class TestBase constructor() {
     /*
      * In common tests we emulate parameterized tests
@@ -33,7 +40,7 @@ public expect open class TestBase constructor() {
         expected: ((Throwable) -> Boolean)? = null,
         unhandled: List<(Throwable) -> Boolean> = emptyList(),
         block: suspend CoroutineScope.() -> Unit
-    )
+    ): TestResult
 }
 
 public suspend inline fun hang(onCancellation: () -> Unit) {

kotlinx-coroutines-core/common/test/flow/operators/FlatMapMergeBaseTest.kt

@@ -90,5 +90,5 @@ abstract class FlatMapMergeBaseTest : FlatMapBaseTest() {
     }
 
     @Test
-    abstract fun testFlatMapConcurrency()
+    abstract fun testFlatMapConcurrency(): TestResult
 }

kotlinx-coroutines-core/js/test/PromiseTest.kt

@@ -74,4 +74,16 @@ class PromiseTest : TestBase() {
         assertSame(d2, deferred)
         assertEquals("OK", d2.await())
     }
-}
+
+    @Test
+    fun testLeverageTestResult(): TestResult {
+        // Cannot use expect(..) here
+        var seq = 0
+        val result = runTest {
+            ++seq
+        }
+        return result.then {
+            if (seq != 1) error("Unexpected result: $seq")
+        }
+    }
+}

kotlinx-coroutines-core/js/test/TestBase.kt

@@ -9,6 +9,9 @@ import kotlin.js.*
 public actual val isStressTest: Boolean = false
 public actual val stressTestMultiplier: Int = 1
 
+@Suppress("ACTUAL_WITHOUT_EXPECT", "ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE")
+public actual typealias TestResult = Promise<Unit>
+
 public actual open class TestBase actual constructor() {
     public actual val isBoundByJsTestTimeout = true
     private var actionIndex = 0
@@ -77,7 +80,7 @@ public actual open class TestBase actual constructor() {
         expected: ((Throwable) -> Boolean)? = null,
         unhandled: List<(Throwable) -> Boolean> = emptyList(),
         block: suspend CoroutineScope.() -> Unit
-    ): dynamic {
+    ): TestResult {
         var exCount = 0
         var ex: Throwable? = null
         /*

kotlinx-coroutines-core/jvm/test/TestBase.kt

@@ -30,6 +30,9 @@ public actual val stressTestMultiplier = stressTestMultiplierSqrt * stressTestMu
 
 public val stressTestMultiplierCbrt = cbrt(stressTestMultiplier.toDouble()).roundToInt()
 
+@Suppress("ACTUAL_WITHOUT_EXPECT")
+public actual typealias TestResult = Unit
+
 /**
  * Base class for tests, so that tests for predictable scheduling of actions in multiple coroutines sharing a single
  * thread can be written. Use it like this:
@@ -188,7 +191,7 @@ public actual open class TestBase actual constructor() {
         expected: ((Throwable) -> Boolean)? = null,
         unhandled: List<(Throwable) -> Boolean> = emptyList(),
         block: suspend CoroutineScope.() -> Unit
-    ) {
+    ): TestResult {
         var exCount = 0
         var ex: Throwable? = null
         try {

kotlinx-coroutines-core/native/test/TestBase.kt

@@ -7,6 +7,9 @@ package kotlinx.coroutines
 public actual val isStressTest: Boolean = false
 public actual val stressTestMultiplier: Int = 1
 
+@Suppress("ACTUAL_WITHOUT_EXPECT")
+public actual typealias TestResult = Unit
+
 public actual open class TestBase actual constructor() {
     public actual val isBoundByJsTestTimeout = false
     private var actionIndex = 0
@@ -71,7 +74,7 @@ public actual open class TestBase actual constructor() {
         expected: ((Throwable) -> Boolean)? = null,
         unhandled: List<(Throwable) -> Boolean> = emptyList(),
         block: suspend CoroutineScope.() -> Unit
-    ) {
+    ): TestResult {
         var exCount = 0
         var ex: Throwable? = null
         try {