Issue#67 Extract JUnit5 MainDispatcher

test-util-junit5-android/build.gradle

@@ -32,4 +32,6 @@ android {
 dependencies {
     implementation "org.junit.jupiter:junit-jupiter-engine:$junit5_version"
     implementation "androidx.arch.core:core-runtime:$arch_core_version"
+
+    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutines_version"
 }

test-util-junit5-android/src/main/java/org/fnives/test/showcase/android/testutil/StandardTestMainDispatcher.kt

@@ -0,0 +1,30 @@
+package org.fnives.test.showcase.android.testutil
+
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.TestDispatcher
+import org.fnives.test.showcase.android.testutil.StandardTestMainDispatcher.Companion.testDispatcher
+
+/**
+ * Custom Junit5 Extension which replaces the main dispatcher with a Standard [TestDispatcher]
+ *
+ * One can access the test dispatcher via [testDispatcher] static getter.
+ */
+@OptIn(ExperimentalCoroutinesApi::class)
+class StandardTestMainDispatcher : TestMainDispatcher() {
+
+    override var createdTestDispatcher: TestDispatcher?
+        get() = privateTestDispatcher
+        set(value) {
+            privateTestDispatcher = value
+        }
+
+    override fun createDispatcher(): TestDispatcher = StandardTestDispatcher()
+
+    companion object {
+        private var privateTestDispatcher: TestDispatcher? = null
+        val testDispatcher: TestDispatcher
+            get() = privateTestDispatcher
+                ?: throw IllegalStateException("StandardTestMainDispatcher is in afterEach State")
+    }
+}

test-util-junit5-android/src/main/java/org/fnives/test/showcase/android/testutil/TestMainDispatcher.kt

@@ -0,0 +1,32 @@
+package org.fnives.test.showcase.android.testutil
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.TestDispatcher
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.setMain
+import org.junit.jupiter.api.extension.AfterEachCallback
+import org.junit.jupiter.api.extension.BeforeEachCallback
+import org.junit.jupiter.api.extension.ExtensionContext
+
+/**
+ * Custom Junit5 Extension which replaces the main dispatcher with a [TestDispatcher]
+ */
+@OptIn(ExperimentalCoroutinesApi::class)
+abstract class TestMainDispatcher : BeforeEachCallback, AfterEachCallback {
+
+    protected abstract var createdTestDispatcher: TestDispatcher?
+
+    abstract fun createDispatcher() : TestDispatcher
+
+    final override fun beforeEach(context: ExtensionContext?) {
+        val testDispatcher = createDispatcher()
+        createdTestDispatcher = testDispatcher
+        Dispatchers.setMain(testDispatcher)
+    }
+
+    final override fun afterEach(context: ExtensionContext?) {
+        Dispatchers.resetMain()
+        createdTestDispatcher = null
+    }
+}

test-util-junit5-android/src/main/java/org/fnives/test/showcase/android/testutil/UnconfinedTestMainDispatcher.kt

@@ -0,0 +1,30 @@
+package org.fnives.test.showcase.android.testutil
+
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.TestDispatcher
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
+import org.fnives.test.showcase.android.testutil.UnconfinedTestMainDispatcher.Companion.testDispatcher
+
+/**
+ * Custom Junit5 Extension which replaces the main dispatcher with a Unconfined [TestDispatcher]
+ *
+ * One can access the test dispatcher via [testDispatcher] static getter.
+ */
+@OptIn(ExperimentalCoroutinesApi::class)
+class UnconfinedTestMainDispatcher : TestMainDispatcher() {
+
+    override var createdTestDispatcher: TestDispatcher?
+        get() = privateTestDispatcher
+        set(value) {
+            privateTestDispatcher = value
+        }
+
+    override fun createDispatcher(): TestDispatcher = UnconfinedTestDispatcher()
+
+    companion object {
+        private var privateTestDispatcher: TestDispatcher? = null
+        val testDispatcher: TestDispatcher
+            get() = privateTestDispatcher
+                ?: throw IllegalStateException("StandardTestMainDispatcher is in afterEach State")
+    }
+}