attempt to fix IT tests

Author: ldetmer

google-cloud-spanner/src/test/java/com/google/cloud/spanner/connection/it/ITMutableCredentialsTest.java

@@ -41,8 +41,8 @@
 @Category(SerialIntegrationTest.class)
 @RunWith(JUnit4.class)
 public class ITMutableCredentialsTest extends ITAbstractSpannerTest {
-  private static final String INVALID_KEY_FILE =
-      ITMutableCredentialsTest.class.getResource("test-key.json").getPath();
+  private static final String INVALID_KEY_RESOURCE =
+      "/com/google/cloud/spanner/connection/test-key.json";
 
   @Test
   public void testMutableCredentialsUpdateAuthorizationForRunningClient() throws IOException {
@@ -58,7 +58,8 @@ public void testMutableCredentialsUpdateAuthorizationForRunningClient() throws I
 
     ServiceAccountCredentials validCredentials = (ServiceAccountCredentials) credentialsFromFile;
     ServiceAccountCredentials invalidCredentials;
-    try (InputStream stream = Files.newInputStream(Paths.get(INVALID_KEY_FILE))) {
+    try (InputStream stream = ITMutableCredentialsTest.class.getResourceAsStream(INVALID_KEY_RESOURCE)) {
+      assertNotNull("Missing test resource: " + INVALID_KEY_RESOURCE, stream);
       invalidCredentials = ServiceAccountCredentials.fromStream(stream);
     }