Issue#67 Extract MainDispatcherTestRule into Library

test-util-android/src/main/java/org/fnives/test/showcase/android/testutil/synchronization/MainDispatcherTestRule.kt

@@ -0,0 +1,64 @@
+package org.fnives.test.showcase.android.testutil.synchronization
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestDispatcher
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.setMain
+import org.fnives.test.showcase.android.testutil.synchronization.idlingresources.anyResourceIdling
+import org.fnives.test.showcase.android.testutil.synchronization.idlingresources.awaitIdlingResources
+import org.junit.rules.TestRule
+import org.junit.runner.Description
+import org.junit.runners.model.Statement
+
+@OptIn(ExperimentalCoroutinesApi::class)
+open class MainDispatcherTestRule(private val useStandard: Boolean = true) : TestRule {
+
+    private lateinit var testDispatcher: TestDispatcher
+
+    override fun apply(base: Statement, description: Description): Statement =
+        object : Statement() {
+            @Throws(Throwable::class)
+            override fun evaluate() {
+                val dispatcher = if (useStandard) StandardTestDispatcher() else UnconfinedTestDispatcher()
+                Dispatchers.setMain(dispatcher)
+                testDispatcher = dispatcher
+                onTestDispatcherInitialized(testDispatcher)
+                try {
+                    base.evaluate()
+                } finally {
+                    Dispatchers.resetMain()
+                    onTestDispatcherReset()
+                }
+            }
+        }
+
+    open fun onTestDispatcherInitialized(testDispatcher: TestDispatcher) = Unit
+
+    open fun onTestDispatcherReset() = Unit
+
+    fun advanceUntilIdleWithIdlingResources() = runOnUIAwaitOnCurrent {
+        testDispatcher.advanceUntilIdleWithIdlingResources()
+    }
+
+    fun advanceUntilIdle() = runOnUIAwaitOnCurrent {
+        testDispatcher.scheduler.advanceUntilIdle()
+    }
+
+    fun advanceTimeBy(delayInMillis: Long) = runOnUIAwaitOnCurrent {
+        testDispatcher.scheduler.advanceTimeBy(delayInMillis)
+    }
+
+    companion object {
+        fun TestDispatcher.advanceUntilIdleWithIdlingResources() {
+            scheduler.advanceUntilIdle() // advance until a request is sent
+            while (anyResourceIdling()) { // check if any request is in progress
+                awaitIdlingResources() // complete all requests and other idling resources
+                scheduler.advanceUntilIdle() // run coroutines after request is finished
+            }
+            scheduler.advanceUntilIdle()
+        }
+    }
+}