Add unit tests

src/main/java/com/google/firebase/appcheck/FirebaseAppCheckClientImpl.java

@@ -56,11 +56,6 @@ static Builder builder() {
 
   @Override
   public VerifyAppCheckTokenResponse verifyToken(String token) throws FirebaseAppCheckException {
-    // Verify Token payload
-    // Verify token signature
-    // return the decoded token
-    // new DecodedAppCheckToken(payload)
-    // new VerifyAppCheckTokenResponse(token)
     DecodedAppCheckToken decodedAppCheckToken = tokenVerifier.verifyToken(token);
     return new VerifyAppCheckTokenResponse(decodedAppCheckToken);
   }

src/test/java/com/google/firebase/appcheck/FirebaseAppCheckTest.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * 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
+ *
+ *     http://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.firebase.appcheck;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.FirebaseOptions;
+import com.google.firebase.TestOnlyImplFirebaseTrampolines;
+import com.google.firebase.auth.MockGoogleCredentials;
+import org.junit.After;
+import org.junit.Test;
+
+public class FirebaseAppCheckTest {
+
+  private static final FirebaseOptions TEST_OPTIONS = FirebaseOptions.builder()
+          .setCredentials(new MockGoogleCredentials("test-token"))
+          .setProjectId("test-project")
+          .build();
+
+  @After
+  public void tearDown() {
+    TestOnlyImplFirebaseTrampolines.clearInstancesForTest();
+  }
+
+  @Test
+  public void testGetInstance() {
+    FirebaseApp.initializeApp(TEST_OPTIONS);
+
+    FirebaseAppCheck appCheck = FirebaseAppCheck.getInstance();
+
+    assertSame(appCheck, FirebaseAppCheck.getInstance());
+  }
+
+  @Test
+  public void testGetInstanceByApp() {
+    FirebaseApp app = FirebaseApp.initializeApp(TEST_OPTIONS, "custom-app");
+
+    FirebaseAppCheck appCheck = FirebaseAppCheck.getInstance(app);
+
+    assertSame(appCheck, FirebaseAppCheck.getInstance(app));
+  }
+
+  @Test
+  public void testDefaultAppCheckClient() {
+    FirebaseApp app = FirebaseApp.initializeApp(TEST_OPTIONS, "custom-app");
+    FirebaseAppCheck appCheck = FirebaseAppCheck.getInstance(app);
+
+    FirebaseAppCheckClient client = appCheck.getAppCheckClient();
+
+    assertTrue(client instanceof FirebaseAppCheckClientImpl);
+    assertSame(client, appCheck.getAppCheckClient());
+  }
+
+  @Test
+  public void testAppDelete() {
+    FirebaseApp app = FirebaseApp.initializeApp(TEST_OPTIONS, "custom-app");
+    FirebaseAppCheck appCheck = FirebaseAppCheck.getInstance(app);
+    assertNotNull(appCheck);
+
+    app.delete();
+
+    try {
+      FirebaseAppCheck.getInstance(app);
+      fail("No error thrown when getting app check instance after deleting app");
+    } catch (IllegalStateException expected) {
+      // expected
+    }
+  }
+
+  @Test
+  public void testAppCheckClientWithoutProjectId() {
+    FirebaseOptions options = FirebaseOptions.builder()
+            .setCredentials(new MockGoogleCredentials("test-token"))
+            .build();
+    FirebaseApp.initializeApp(options);
+
+    try {
+      FirebaseAppCheck.getInstance();
+      fail("No error thrown for missing project ID");
+    } catch (IllegalArgumentException expected) {
+      String message = "Project ID is required to access App Check service. Use a service "
+              + "account credential or set the project ID explicitly via FirebaseOptions. "
+              + "Alternatively you can also set the project ID via the GOOGLE_CLOUD_PROJECT "
+              + "environment variable.";
+      assertEquals(message, expected.getMessage());
+    }
+  }
+}