Added basic unit test for AtomicExecutor

chat-android/src/test/java/com/ably/chat/AtomicExecutorTest.kt

@@ -0,0 +1,26 @@
+package com.ably.chat
+
+import java.util.concurrent.Executors
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.asCoroutineDispatcher
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.test.runTest
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class AtomicExecutorTest {
+
+    @Test
+    fun `should perform given operation`() = runTest {
+        val singleThreadedDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
+        val atomicExecutor = AtomicExecutor(CoroutineScope(singleThreadedDispatcher))
+        val deferred = atomicExecutor.execute {
+            delay(5000)
+            return@execute "Hello"
+        }
+        val result = deferred.receive()
+        assert(result.isSuccess)
+        assertEquals("Hello", result.getOrNull())
+    }
+}