Add MviTurbineExtension to simplify test setup

core/ui/compose/testing/src/main/kotlin/app/k9mail/core/ui/compose/testing/mvi/MviTurbineExtension.kt

@@ -0,0 +1,85 @@
+package app.k9mail.core.ui.compose.testing.mvi
+
+import app.cash.turbine.ReceiveTurbine
+import app.cash.turbine.testIn
+import app.k9mail.core.ui.compose.common.mvi.UnidirectionalViewModel
+import assertk.Assert
+import assertk.all
+import assertk.assertThat
+import assertk.assertions.isEqualTo
+import kotlinx.coroutines.CoroutineScope
+
+/**
+ * The `turbines` extension function creates a MviTurbines instance for the given MVI ViewModel.
+ */
+inline fun <reified STATE, EVENT, EFFECT> UnidirectionalViewModel<STATE, EVENT, EFFECT>.turbines(
+    coroutineScope: CoroutineScope,
+): MviTurbines<STATE, EFFECT> {
+    return MviTurbines(
+        stateTurbine = state.testIn(coroutineScope),
+        effectTurbine = effect.testIn(coroutineScope),
+    )
+}
+
+/**
+ * The `turbinesWithInitialStateCheck` extension function creates a MviTurbines instance for the given MVI ViewModel
+ * and ensures that the initial state is emitted.
+ */
+suspend inline fun <reified STATE, EVENT, EFFECT>
+    UnidirectionalViewModel<STATE, EVENT, EFFECT>.turbinesWithInitialStateCheck(
+        coroutineScope: CoroutineScope,
+        initialState: STATE,
+    ): MviTurbines<STATE, EFFECT> {
+    val turbines = MviTurbines(
+        stateTurbine = state.testIn(coroutineScope),
+        effectTurbine = effect.testIn(coroutineScope),
+    )
+
+    assertThatAndMviTurbinesConsumed(
+        actual = turbines.stateTurbine.awaitItem(),
+        turbines = turbines,
+    ) {
+        isEqualTo(initialState)
+    }
+
+    return turbines
+}
+
+/**
+ * The `assertThatAndMviTurbinesConsumed` function ensures that the assertion passed and
+ * all events in the given MviTurbines have been consumed.
+ *
+ * Usage:
+ *  val actualValue: T = getActualValue()
+ *  val turbines = viewModel.turbines(coroutineScope)
+ *  assertThatAndMviTurbinesConsumed(actualValue, turbines) {
+ *     // your assertion here
+ *  }
+ *
+ *  @param T The type of the actual value.
+ *  @param STATE The type of the state.
+ *  @param EFFECT The type of the effect.
+ *  @param actual The actual value being asserted.
+ *  @param turbines The MviTurbines instance to check if all events are consumed.
+ *  @param assertion An extension function on `Assert<T>`, which is used to define assertions on the actual value.
+ */
+fun <T, STATE, EFFECT> assertThatAndMviTurbinesConsumed(
+    actual: T,
+    turbines: MviTurbines<STATE, EFFECT>,
+    assertion: Assert<T>.() -> Unit,
+) {
+    assertThat(actual).all {
+        assertion()
+    }
+
+    turbines.stateTurbine.ensureAllEventsConsumed()
+    turbines.effectTurbine.ensureAllEventsConsumed()
+}
+
+/**
+ * A container class for the state and effect turbines of an MVI ViewModel.
+ */
+data class MviTurbines<STATE, EFFECT>(
+    val stateTurbine: ReceiveTurbine<STATE>,
+    val effectTurbine: ReceiveTurbine<EFFECT>,
+)