TestService: Add cros_signing tests endpoint.

BUG=chromium:992927
TEST=run_tests, manually ran endpoint

Change-Id: I22bd6a81113c973809330d7cdc0e7e5899ce6eb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1757097
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
diff --git a/api/controller/test_unittest.py b/api/controller/test_unittest.py
index 49f3615..4a4caaf 100644
--- a/api/controller/test_unittest.py
+++ b/api/controller/test_unittest.py
@@ -128,6 +128,16 @@
     self.assertFalse(output_msg.failed_packages)
 
 
+class CrosSigningTestTest(cros_test_lib.RunCommandTestCase,
+                          api_config.ApiConfigMixin):
+  """CrosSigningTest tests."""
+
+  def testValidateOnly(self):
+    """Sanity check that a validate only call does not execute any logic."""
+    test_controller.CrosSigningTest(None, None, self.validate_only_config)
+    self.assertFalse(self.rc.call_count)
+
+
 class VmTestTest(cros_test_lib.RunCommandTestCase, api_config.ApiConfigMixin):
   """Test the VmTest endpoint."""