Combining ContainerEq and DoubleEq matchers in gtest - googletest

Question

Is there a way to assert double values of containers in gtest using DoubleNear matcher?
There is also a CombiningMatcher<T> in the codebase but I cannot crack how to use it.
For example I would like to achieve something like that:
std::array<double, 2> expected{1.23, 2.34};
std::array<double, 2> results{1.231, 2.341};
ASSERT_THAT(results, ContainerEq(DoubleNear(expected, 1e-3)));
Where for each container item a DoubleNear is applied.
Another way would be to use PointWise matcher, which would work like:
ASSERT_THAT(results, Pointwise(DoubleNear(1e-3), expected));
Googletest version 1.10 is used.

Answer 1

I don't know if there is a way in gtest 1.10 to directly use container matcher with floating point matcher (though it sounds like a reasonable feature request). For now you can define your own container matcher that takes abs err as an additional argument and internally compares container elements using testing::DoubleNear matcher:
MATCHER_P2(ContainerDoubleNear, container, abs_err, "")
{
if (container.size() != arg.size()) return false;
for (int i = 0; i < container.size(); i++)
{
if (!::testing::ExplainMatchResult(::testing::DoubleNear(arg[i], abs_err), container[i], result_listener))
{
*result_listener << " for element at idx " << i;
return false;
}
}
return true;
}
You can then use it like that:
EXPECT_THAT(expected, ContainerDoubleNear(results, ABS_ERR));
Live demo, diagnostic message might be slightly improved.