This commit will improve the accuracy of `filter_test.go` unit tests.
Before reflect.DeepEqual was used to check equality between slices,
but `f.filtered` and `sort.StringSlice` aren't comparable.
There was also a bug where `reflect.DeepEqual`
was returning `false` but the test did not fail due to wrong `if` check.
Use gomega to simplify assertions.
Signed-off-by: Rishi <rishnai1@in.ibm.com>