Create `InMemoryDataStore` class

core/datastore-test/src/main/kotlin/com/google/samples/apps/nowinandroid/core/datastore/test/InMemoryDataStore.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.core.datastore.test
+
+import androidx.datastore.core.DataStore
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.updateAndGet
+
+class InMemoryDataStore<T>(initialValue: T) : DataStore<T> {
+    override val data = MutableStateFlow(initialValue)
+    override suspend fun updateData(
+        transform: suspend (it: T) -> T,
+    ) = data.updateAndGet { transform(it) }
+}