googletest: Add a flag to fail if no tests were selected to run.

There are two cases that prompt this behavior:

- All test cases in the binary are disabled.

- There are more shards defined than test cases, so some shards are empty.

The result in each case is the same: the test runner needs to spin up
additional processes that do nothing, which is wasteful, especially when tests
need expensive resources.

PiperOrigin-RevId: 769176856
Change-Id: Ifa399a0b7b68e4add5a94ca148b32b2938a8666d

docs/advanced.md

@@ -1940,6 +1940,21 @@ test case is linked in.
 Note that *any* test case linked in makes the program valid for the purpose of
 this check. In particular, even a disabled test case suffices.
 
+### Enforcing Running At Least One Test Case
+
+In addition to enforcing that tests are defined in the binary with
+`--gtest_fail_if_no_test_linked`, it is also possible to enforce that a test
+case was actually executed to ensure that resources are not consumed by tests
+that do nothing.
+
+To catch such optimization opportunities, run the test program with the
+`--gtest_fail_if_no_test_selected` flag or set the
+`GTEST_FAIL_IF_NO_TEST_SELECTED` environment variable to a value other than `0`.
+
+A test is considered selected if it begins to run, even if it is later skipped
+via `GTEST_SKIP`. Thus, `DISABLED` tests do not count as selected and neither do
+tests that are not matched by `--gtest_filter`.
+
 ### Repeating the Tests
 
 Once in a while you'll run into a test whose result is hit-or-miss. Perhaps it

googletest/src/gtest.cc

@@ -269,6 +269,13 @@ GTEST_DEFINE_bool_(
     "True if and only if the test should fail if no test case (including "
     "disabled test cases) is linked.");
 
+GTEST_DEFINE_bool_(
+    fail_if_no_test_selected,
+    testing::internal::BoolFromGTestEnv("fail_if_no_test_selected", false),
+    "True if and only if the test should fail if no test case is selected to "
+    "run. A test case is selected to run if it is not disabled and is matched "
+    "by the filter flag so that it starts executing.");
+
 GTEST_DEFINE_bool_(
     also_run_disabled_tests,
     testing::internal::BoolFromGTestEnv("also_run_disabled_tests", false),
@@ -6079,6 +6086,14 @@ bool UnitTestImpl::RunAllTests() {
                       TearDownEnvironment);
         repeater->OnEnvironmentsTearDownEnd(*parent_);
       }
+    } else if (GTEST_FLAG_GET(fail_if_no_test_selected)) {
+      // If there were no tests to run, bail if we were requested to be strict.
+      constexpr char kNoTestsSelectedMessage[] =
+          "No tests were selected to run. Please make sure at least one test "
+          "exists and is not disabled! If the test is sharded, you may have "
+          "defined more shards than test cases, which is wasteful.";
+      ColoredPrintf(GTestColor::kRed, "%s\n", kNoTestsSelectedMessage);
+      return false;
     }
 
     elapsed_time_ = timer.Elapsed();
@@ -6763,6 +6778,7 @@ static bool ParseGoogleTestFlag(const char* const arg) {
   GTEST_INTERNAL_PARSE_FLAG(death_test_use_fork);
   GTEST_INTERNAL_PARSE_FLAG(fail_fast);
   GTEST_INTERNAL_PARSE_FLAG(fail_if_no_test_linked);
+  GTEST_INTERNAL_PARSE_FLAG(fail_if_no_test_selected);
   GTEST_INTERNAL_PARSE_FLAG(filter);
   GTEST_INTERNAL_PARSE_FLAG(internal_run_death_test);
   GTEST_INTERNAL_PARSE_FLAG(list_tests);

googletest/test/googletest-fail-if-no-test-linked-test.py

@@ -80,11 +80,7 @@ class GTestFailIfNoTestLinkedTest(gtest_test_utils.TestCase):
         )
     )
     warning_file_contents = open(warning_file, "r").read()
-    self.assertEqual(
-        warning_file_contents,
-        "This test program does NOT link in any test case. Please make sure"
-        " this is intended.\n",
-    )
+    self.assertIn("does NOT link", warning_file_contents)
 
   def testFailsIfNoTestLinkedAndFlagSpecified(self):
     """Tests the behavior of no test linked and flag specified."""

googletest/test/googletest-fail-if-no-test-selected-test.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python3  # pylint: disable=g-interpreter-mismatch
+#
+# Copyright 2025, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+"""Tests for Google Test's --gtest_fail_if_no_test_selected flag."""
+
+from googletest.test import gtest_test_utils
+
+
+# The command line flag for enabling the fail-if-no-test-selected behavior.
+FAIL_IF_NO_TEST_SELECTED_FLAG = "gtest_fail_if_no_test_selected"
+
+# The environment variable for the test output warnings file.
+TEST_WARNINGS_OUTPUT_FILE = "TEST_WARNINGS_OUTPUT_FILE"
+
+
+class GTestFailIfNoTestSelectedTest(gtest_test_utils.TestCase):
+  """Tests the --gtest_fail_if_no_test_selected flag."""
+
+  def Run(self, program_name, flags=None, env=None):
+    """Run the given program with the given flag.
+
+    Args:
+      program_name: Name of the program to run.
+      flags: The command line flags to pass to the program, or None.
+      env: Dictionary with environment to pass to the subprocess.
+
+    Returns:
+      True if the program exits with code 0, false otherwise.
+    """
+
+    exe_path = gtest_test_utils.GetTestExecutablePath(program_name)
+    args = [exe_path]
+    if flags is not None:
+      args.extend(flags)
+    process = gtest_test_utils.Subprocess(args, capture_stderr=False, env=env)
+    return process.exited and process.exit_code == 0
+
+  def testSucceedsWhenFlagIsNotSetAndOnlyDisabledTestsPresent(self):
+    """Tests that no test selected results in success without the flag set."""
+    self.assertTrue(
+        self.Run("googletest-fail-if-no-test-linked-test-with-disabled-test_"),
+    )
+
+  def testFailsWhenFlagIsSetAndOnlyDisabledTestsPresent(self):
+    """Tests that no test selected results in failure with the flag set."""
+    self.assertFalse(
+        self.Run(
+            "googletest-fail-if-no-test-linked-test-with-disabled-test_",
+            flags=[f"--{FAIL_IF_NO_TEST_SELECTED_FLAG}"],
+        ),
+    )
+
+  def testSucceedsWhenFlagIsSetAndEnabledTestsPresent(self):
+    """Tests that a test running still succeeds when the flag is set."""
+    self.assertTrue(
+        self.Run(
+            "googletest-fail-if-no-test-linked-test-with-enabled-test_",
+            flags=[f"--{FAIL_IF_NO_TEST_SELECTED_FLAG}"],
+        ),
+    )
+
+
+if __name__ == "__main__":
+  gtest_test_utils.Main()