kokoro: add a light lint+test mode

To help reproduce kokoro failures locally, add an explicit mode that
only runs lint & unittests, and never builds the plugin.

Change-Id: Ia5ea6f146e16225247ca4dc6f83402c265875469
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/6202067
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>

Author: vapier

kokoro/build

@@ -50,6 +50,12 @@ DEPOT_TOOLS_URI = "https://chromium.googlesource.com/chromium/tools/depot_tools"
 DEPOT_TOOLS_DIR = kokoro.LIBAPPS_DIR / "depot_tools"
 
 
+def is_lint_test_only() -> bool:
+    """Whether we're only linting+testing the current tree."""
+    # This env var is passed down by our script.
+    return bool(os.environ.get("LIBAPPS_LINT_TEST"))
+
+
 def is_presubmit():
     """Whether we're testing a pending CL."""
     # This env var is passed down by kokoro.
@@ -65,6 +71,10 @@ def should_build_plugin():
     """
     logging.info("Detecting whether to build plugin")
 
+    if is_lint_test_only():
+        logging.info("Only running lint+unittest")
+        return False
+
     # Release builders always build the plugin.
     if not is_presubmit():
         logging.info("Release builder: always building the plugin!")

kokoro/container

@@ -138,6 +138,8 @@ def run_docker(opts, docker_args=(), cmd_args=()):
     # The kokoro build detects this env var for presubmit.
     if opts.type == "presubmit":
         base_cmd += ["--env", "KOKORO_GERRIT_REVISION=HEAD"]
+    elif opts.type == "lint-test":
+        base_cmd += ["--env", "LIBAPPS_LINT_TEST=false"]
 
     cmd = base_cmd + list(docker_args) + [CONTAINER_NAME] + list(cmd_args)
     return sudo_run(opts, cmd, cwd=libdot.LIBAPPS_DIR, check=False)
@@ -173,7 +175,7 @@ def get_parser():
     )
     parser.add_argument(
         "--type",
-        choices=("presubmit", "release"),
+        choices=("lint-test", "presubmit", "release"),
         default="presubmit",
         help="Type of build to run (default: %(default)s)",
     )