add test for old behavior (dispatches when needed)

Author: murfel

kotlinx-coroutines-core/common/test/flow/channels/ChannelFlowTest.kt

@@ -222,4 +222,19 @@ class ChannelFlowTest : TestBase() {
         }
         expect(4)
     }
+
+    @Test
+    fun testDispatchesToDifferentDispatcherWhenCollected() = runTest {
+        expect(1)
+        val myFlow = flow<Int> {
+            finish(4)
+        }.flowOn(wrapperDispatcher())
+        launch(start = CoroutineStart.UNDISPATCHED) {
+            expect(2)
+            myFlow.collectLatest {
+                expectUnreached()
+            }
+        }
+        expect(3)
+    }
 }