fix: fixed compilation warnings from error prone

* Fixed equals check to compare against other instead of self
* Added annotation to ignore error prone warning (Details here: https://errorprone.info/bugpattern/TruthSelfEquals)
* Fixed EqualsTester usage (details on usage error here https://errorprone.info/bugpattern/MissingTestCall, proper usage described at https://www.javadoc.io/doc/com.google.guava/guava-testlib/21.0/com/google/common/testing/EqualsTester.html)
* Added missing assertion

google-cloud-core/src/main/java/com/google/cloud/ServiceOptions.java

@@ -697,7 +697,7 @@ protected boolean baseEquals(ServiceOptions<?, ?> other) {
         && Objects.equals(retrySettings, other.retrySettings)
         && Objects.equals(serviceFactoryClassName, other.serviceFactoryClassName)
         && Objects.equals(serviceRpcFactoryClassName, other.serviceRpcFactoryClassName)
-        && Objects.equals(clock, clock)
+        && Objects.equals(clock, other.clock)
         && Objects.equals(quotaProjectId, other.quotaProjectId);
   }
 

google-cloud-core/src/test/java/com/google/cloud/BaseServiceExceptionTest.java

@@ -140,6 +140,7 @@ public void testTranslateAndThrow() throws Exception {
   }
 
   @Test
+  @SuppressWarnings("TruthSelfEquals")
   public void testError_Equal() {
     BaseServiceException.Error error = new BaseServiceException.Error(0, "reason", true);
     assertThat(error).isEqualTo(error);

google-cloud-core/src/test/java/com/google/cloud/DateTest.java

@@ -126,9 +126,7 @@ public void equalAndHashCode() {
     Date d1 = Date.fromYearMonthDay(2016, 9, 18);
     Date d2 = Date.fromYearMonthDay(2016, 9, 18);
     Date d3 = Date.fromYearMonthDay(2016, 9, 19);
-    EqualsTester tester = new EqualsTester();
-    tester.addEqualityGroup(d1, d2);
-    tester.addEqualityGroup(d3);
+    new EqualsTester().addEqualityGroup(d1, d2).addEqualityGroup(d3).testEquals();
   }
 
   @Test

google-cloud-core/src/test/java/com/google/cloud/StringEnumTest.java

@@ -101,13 +101,12 @@ public void testValueOfStrict() {
 
   @Test
   public void testEquals() {
-    EqualsTester tester = new EqualsTester();
-
-    tester.addEqualityGroup(Letter.A, Letter.valueOf("A"), Letter.valueOfStrict("A"));
-    tester.addEqualityGroup(Letter.B, Letter.valueOf("B"), Letter.valueOfStrict("B"));
-    tester.addEqualityGroup(Letter.C, Letter.valueOf("C"), Letter.valueOfStrict("C"));
-    tester.addEqualityGroup(
-        Letter.valueOf("NonExistentLetter"), Letter.valueOf("NonExistentLetter"));
+    new EqualsTester()
+        .addEqualityGroup(Letter.A, Letter.valueOf("A"), Letter.valueOfStrict("A"))
+        .addEqualityGroup(Letter.B, Letter.valueOf("B"), Letter.valueOfStrict("B"))
+        .addEqualityGroup(Letter.C, Letter.valueOf("C"), Letter.valueOfStrict("C"))
+        .addEqualityGroup(Letter.valueOf("NonExistentLetter"), Letter.valueOf("NonExistentLetter"))
+        .testEquals();
   }
 
   @Test
@@ -123,6 +122,7 @@ public void testValueOfStrict_invalid() {
   @Test
   public void testValues() {
     assertThat(
-        Arrays.asList(Letter.values()).containsAll(Arrays.asList(Letter.A, Letter.B, Letter.C)));
+            Arrays.asList(Letter.values()).containsAll(Arrays.asList(Letter.A, Letter.B, Letter.C)))
+        .isTrue();
   }
 }