Expects that the subject of this
expectation (a Map) contains the given key.
Return
an Expect for the subject of this
expectation.
Since
0.17.0
Samples
expect(mapOf(1 to "a")).toContainKey(1)
fails { // because the map does not contain a key that equals 2
expect(mapOf(1 to "a")).toContainKey(2)
}