message: CreateTestFile doesn't need to crash on failure.
  An expectation should, for all existing cases, work fine. This may result in later assertions also failing, but it should be fairly benign.
diff: @@ -36,7 +36,7 @@ namespace {
  string CreateTestFile(Env* env, const string& filename, int length) {
  string input(length, 0);
  for (int i = 0; i < length; i++) input[i] = i;
  - TF_CHECK_OK(WriteStringToFile(env, filename, input));
  + TF_EXPECT_OK(WriteStringToFile(env, filename, input));
  return input;
  }
  