Minor code clean up

src/main/java/com/google/firebase/FirebaseApp.java

@@ -188,7 +188,8 @@ public static FirebaseApp initializeApp(String name) {
     try {
       return initializeApp(getOptionsFromEnvironment(), name);
     } catch (IOException e) {
-      throw new IllegalArgumentException("Failed to load settings from the environment", e);
+      throw new IllegalArgumentException(
+          "Failed to load settings from the system's environment variables", e);
     }
   }
 

src/main/java/com/google/firebase/auth/FirebaseAuth.java

@@ -131,7 +131,7 @@ public static synchronized FirebaseAuth getInstance(FirebaseApp app) {
    * @return A Firebase custom token string.
    * @throws IllegalArgumentException If the specified uid is null or empty, or if the app has not
    *     been initialized with service account credentials.
-   * @throws FirebaseAuthException If an error occurs while minting the custom token.
+   * @throws FirebaseAuthException If an error occurs while generating the custom token.
    */
   public String createCustomToken(@NonNull String uid) throws FirebaseAuthException {
     return createCustomToken(uid, null);
@@ -154,7 +154,7 @@ public String createCustomToken(@NonNull String uid) throws FirebaseAuthExceptio
    * @return A Firebase custom token string.
    * @throws IllegalArgumentException If the specified uid is null or empty, or if the app has not
    *     been initialized with service account credentials.
-   * @throws FirebaseAuthException If an error occurs while minting the custom token.
+   * @throws FirebaseAuthException If an error occurs while generating the custom token.
    */
   public String createCustomToken(@NonNull String uid,
       @Nullable Map<String, Object> developerClaims) throws FirebaseAuthException {
@@ -213,7 +213,8 @@ public String execute() throws FirebaseAuthException {
               serviceAccount.getClientEmail(),
               serviceAccount.getPrivateKey());
         } catch (GeneralSecurityException | IOException e) {
-          throw new FirebaseAuthException(ERROR_CUSTOM_TOKEN, "Failed to mint a custom token", e);
+          throw new FirebaseAuthException(ERROR_CUSTOM_TOKEN,
+              "Failed to generate a custom token", e);
         }
       }
     };

src/test/java/com/google/firebase/internal/CallableOperationTest.java

@@ -17,6 +17,8 @@
 package com.google.firebase.internal;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
@@ -36,7 +38,6 @@
 public class CallableOperationTest {
 
   private static final String TEST_FIREBASE_THREAD = "test-firebase-thread";
-  private static final String SAME_THREAD = "same-thread";
   private static final FirebaseOptions OPTIONS = new Builder()
       .setCredentials(new MockGoogleCredentials())
       .setThreadManager(new MockThreadManager())
@@ -50,40 +51,32 @@ public void tearDown() {
   @Test
   public void testCallResult() throws Exception {
     FirebaseApp app = FirebaseApp.initializeApp(OPTIONS);
-    CallableOperation<String,Exception> operation = new CallableOperation<String, Exception>() {
+    CallableOperation<Boolean,Exception> operation = new CallableOperation<Boolean, Exception>() {
       @Override
-      protected String execute() throws Exception {
+      protected Boolean execute() throws Exception {
         String threadName = Thread.currentThread().getName();
-        if (TEST_FIREBASE_THREAD.equals(threadName)) {
-          return threadName;
-        }
-        return SAME_THREAD;
+        return TEST_FIREBASE_THREAD.equals(threadName);
       }
     };
-    assertEquals(SAME_THREAD, operation.call());
-    assertEquals(TEST_FIREBASE_THREAD, operation.callAsync(app).get());
+    assertFalse(operation.call());
+    assertTrue(operation.callAsync(app).get());
   }
 
   @Test
   public void testCallException() throws Exception {
     FirebaseApp app = FirebaseApp.initializeApp(OPTIONS);
-    CallableOperation<String,Exception> operation = new CallableOperation<String, Exception>() {
+    CallableOperation<Boolean,Exception> operation = new CallableOperation<Boolean, Exception>() {
       @Override
-      protected String execute() throws Exception {
+      protected Boolean execute() throws Exception {
         String threadName = Thread.currentThread().getName();
         if (TEST_FIREBASE_THREAD.equals(threadName)) {
           throw new Exception(threadName);
         }
-        throw new Exception(SAME_THREAD);
+        return false;
       }
     };
-    try {
-      operation.call();
-      fail("No exception thrown");
-    } catch (Exception e) {
-      assertEquals(SAME_THREAD, e.getMessage());
-    }
 
+    assertFalse(operation.call());
     try {
       operation.callAsync(app).get();
       fail("No exception thrown");