Move Imm.Obj. hash code stripping into utility fx

Spotted this functionality in one of mcilwain's test classes that could
be useful to other CommandTestCases when comparing ImmutableObject
output.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=128686426

javatests/google/registry/tools/CommandTestCase.java

@@ -147,6 +147,15 @@ public abstract class CommandTestCase<C extends Command> {
     return ofy().load().type(PollMessage.class).count();
   }
 
+  /**
+   * Asserts whether standard out matches an expected string, allowing for differences in
+   * ImmutableObject hash codes (i.e. "(@1234567)").
+   */
+  protected void assertStdoutForImmutableObjectIs(String expected) throws Exception {
+    assertThat(stripImmutableObjectHashCodes(getStdoutAsString()).trim())
+        .isEqualTo(stripImmutableObjectHashCodes(expected).trim());
+  }
+
   protected void assertStdoutIs(String expected) throws Exception {
     assertThat(getStdoutAsString()).isEqualTo(expected);
   }
@@ -177,6 +186,10 @@ public abstract class CommandTestCase<C extends Command> {
     return Splitter.on('\n').omitEmptyStrings().trimResults().splitToList(getStdoutAsString());
   }
 
+  protected String stripImmutableObjectHashCodes(String string) {
+    return string.replaceAll("\\(@\\d+\\)", "(@)");
+  }
+
   @SuppressWarnings("unchecked")
   protected C newCommandInstance() {
     try {