Google Testing Blog: TotT: Making a Perfect Matcher

TotT: Making a Perfect Matcher

Monday, October 05, 2009

by Zhanyong G. Mock Wan in Google Kirkland
Google C++ Mocking Framework matchers can make both your test code and your test output readableIt's easy to create a matcher that does exactly what you want, either by composing from existing matchers or by writing one from scratchcomposite matcherNot(m)mAnyOf(m1, ..., mn)ORAllOf(m1, ..., mn)ANDEXPECT_THAT(new_code, AnyOf(StartsWith(“// Tests”)),
              Not(ContainsRegex(“TODO.*intern”))));
Expected: (starts with “// Tests”) or
          (doesn't contain regular expression “TODO.*intern”)
Actual: “/* TODO: hire an intern. */ int main() {}”
The MATCHER macro lets you define a named matcherMATCHER(IsEven, “”) { return (arg % 2) == 0; }
EXPECT_THAT(paren_num, IsEven())notany codeautomatically generateExpected: is evenYou can also give multiple parameters to a matcher, or customize its description// P2 means the matcher has 2 parameters. Their names are low and high.

MATCHER_P2(InClosedRange, low, high, “is in range [%(low)s, %(high)s]”) {
  return low <= arg && arg <= high;
}
...
EXPECT_THAT(my_age, InClosedRange(adult_min, penalty_to_withdraw_401k)); Expected: is in range [18, 60]
  Actual: 2
Google C++ Mocking Framework uses compiler type inference to “write” the matcher parameter types for youToilet-Friendly Version

2 comments :

liam.listNovember 3, 2009 at 2:53:00 AM PST
I just do not get some of these matchers. Unit tests are meant to be consistent and repeatable, so I would be interested to find why you think there is a need for such matchers as the "in range" and "is even" ?
Surely the tests should be:
given a number x it is guaranteed to give number y. If you can not guarantee the output then it seems the code being tested has a smell, this being that it depends on global state.
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Gil ZilberfeldNovember 11, 2009 at 5:36:00 AM PST
Hi Zhanyong,

My name is Gil Zilberfeld, and with my colleague Roy Osherove, we do a little cast called This week in testing.

This week we mention the new matcher feature, and talk about the Google mocking framework. I invite you to watch. If you like what you see, please talk about us, so more people can enjoy.

Thanks,

Gil Zilberfeld
Typemock
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