message: FileExists(): Add a test for the directory error message.
diff: #include "absl/status/status.h"
  #include "absl/strings/string_view.h"
  +#include "gmock/gmock.h"
  #include "gtest/gtest.h"
  +using testing::HasSubstr;
  +
  #undef EXPECT_OK
  #define EXPECT_OK(value) EXPECT_TRUE((value).ok())
  @@ -142,6 +145,13 @@ TEST(FileUtil, ScopedTestFileEmplace) {
  }
  }
  +TEST(FileUtil, FileExistsDirectoryErrorMessage) {
  + absl::Status s;
  + s = file::FileExists(testing::TempDir());
  + EXPECT_FALSE(s.ok());
  + EXPECT_THAT(s.message(), HasSubstr("is a directory"));
  +}
  +
  TEST(FileUtil, ReadEmptyDirectory) {
  const std::string test_dir = file::JoinPath(testing::TempDir(), "empty_dir");
  ASSERT_TRUE(file::CreateDir(test_dir).ok());
  