Add gTech command to get .app domain info

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127582475

javatests/google/registry/tools/BUILD

@@ -13,7 +13,9 @@ java_library(
     srcs = glob([
         "*.java",
     ]),
-    resources = glob(["testdata/*.*"]),
+    resources = glob([
+        "testdata/*.*",
+    ]),
     deps = [
         "//java/com/google/common/annotations",
         "//java/com/google/common/base",

javatests/google/registry/tools/CommandTestCase.java

@@ -49,7 +49,8 @@ import org.mockito.runners.MockitoJUnitRunner;
 @RunWith(MockitoJUnitRunner.class)
 public abstract class CommandTestCase<C extends Command> {
 
-  private ByteArrayOutputStream stdout = new ByteArrayOutputStream();
+  private final ByteArrayOutputStream stdout = new ByteArrayOutputStream();
+  private final ByteArrayOutputStream stderr = new ByteArrayOutputStream();
 
   protected C command;
 
@@ -71,6 +72,7 @@ public abstract class CommandTestCase<C extends Command> {
     RegistryToolEnvironment.UNITTEST.setup();
     command = newCommandInstance();
     System.setOut(new PrintStream(stdout));
+    System.setErr(new PrintStream(stderr));
   }
 
   void runCommandInEnvironment(RegistryToolEnvironment env, String... args) throws Exception {
@@ -156,6 +158,13 @@ public abstract class CommandTestCase<C extends Command> {
     }
   }
 
+  protected void assertInStderr(String... expected) throws Exception {
+    String stderror = new String(stderr.toByteArray(), UTF_8);
+    for (String line : expected) {
+      assertThat(stderror).contains(line);
+    }
+  }
+
   void assertNotInStdout(String expected) throws Exception {
     assertThat(getStdoutAsString()).doesNotContain(expected);
   }