Adding tests to ServiceManager

instrumentation/src/main/java/io/opentelemetry/android/internal/services/ServiceManager.java

@@ -8,6 +8,7 @@
 import android.content.Context;
 import androidx.annotation.Nullable;
 import androidx.annotation.RestrictTo;
+import androidx.annotation.VisibleForTesting;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -16,7 +17,8 @@ public final class ServiceManager implements Lifecycle {
     private final Map<Class<? extends Service>, Service> services = new HashMap<>();
     @Nullable private static ServiceManager instance;
 
-    private ServiceManager() {}
+    @VisibleForTesting
+    ServiceManager() {}
 
     @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP_PREFIX)
     public static void initialize(Context appContext) {

instrumentation/src/test/java/io/opentelemetry/android/internal/services/ServiceManagerTest.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.android.internal.services;
+
+import static org.junit.jupiter.api.Assertions.fail;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class ServiceManagerTest {
+
+    private ServiceManager serviceManager;
+
+    @BeforeEach
+    void setUp() {
+        serviceManager = new ServiceManager();
+    }
+
+    @Test
+    void addingServices() {
+        FirstService firstService = mock();
+        SecondService secondService = mock();
+
+        serviceManager.addService(firstService);
+        serviceManager.addService(secondService);
+
+        Assertions.assertEquals(firstService, serviceManager.getService(FirstService.class));
+        Assertions.assertEquals(secondService, serviceManager.getService(SecondService.class));
+    }
+
+    @Test
+    void allowOnlyOneServicePerType() {
+        FirstService firstService = mock();
+        FirstService anotherFirstService = mock();
+
+        serviceManager.addService(firstService);
+
+        try {
+            serviceManager.addService(anotherFirstService);
+            fail();
+        } catch (IllegalArgumentException ignored) {
+        }
+    }
+
+    @Test
+    void delegatingStartCall() {
+        FirstService firstService = mock();
+        SecondService secondService = mock();
+        serviceManager.addService(firstService);
+        serviceManager.addService(secondService);
+
+        serviceManager.start();
+
+        verify(firstService).start();
+        verify(secondService).start();
+    }
+
+    @Test
+    void delegatingStopCall() {
+        FirstService firstService = mock();
+        SecondService secondService = mock();
+        serviceManager.addService(firstService);
+        serviceManager.addService(secondService);
+
+        serviceManager.stop();
+
+        verify(firstService).stop();
+        verify(secondService).stop();
+    }
+
+    private static class FirstService implements Service {}
+
+    private static class SecondService implements Service {}
+}