chore: Fix tests

Author: lqiu96

oauth2_http/java/com/google/auth/oauth2/DefaultCredentialsProvider.java

@@ -311,10 +311,12 @@ private final GoogleCredentials tryGetComputeCredentials(HttpTransportFactory tr
     }
     boolean runningOnComputeEngine = ComputeEngineCredentials.isOnGce(transportFactory, this);
     checkedComputeEngine = true;
+    ComputeEngineCredentials.Builder builder =
+        shouldCheckMDSOnInitialization()
+            ? ComputeEngineCredentials.newBuilder()
+            : ComputeEngineCredentials.newTestBuilder();
     if (runningOnComputeEngine) {
-      return ComputeEngineCredentials.newBuilder()
-          .setHttpTransportFactory(transportFactory)
-          .build();
+      return builder.setHttpTransportFactory(transportFactory).build();
     }
     return null;
   }
@@ -363,6 +365,10 @@ InputStream readStream(File file) throws FileNotFoundException {
     return new FileInputStream(file);
   }
 
+  boolean shouldCheckMDSOnInitialization() {
+    return true;
+  }
+
   /*
    * End of methods to allow overriding in the test code to isolate from the environment.
    */

oauth2_http/javatests/com/google/auth/oauth2/DefaultCredentialsProviderTest.java

@@ -977,6 +977,11 @@ InputStream readStream(File file) throws FileNotFoundException {
     void setFileSandbox(boolean fileSandbox) {
       this.fileSandbox = fileSandbox;
     }
+
+    @Override
+    boolean shouldCheckMDSOnInitialization() {
+      return false;
+    }
   }
 
   static class MockRequestCountingTransportFactory implements HttpTransportFactory {