tests: use testify to check the test results

[cpanato]

What type of PR is this?
/kind cleanup

Any specific area of the project related to this PR?
/area tests

What this PR does / why we need it:

Use testify to assert the test results to make more clean and avoid writing more code

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

@cpanato: The label(s) area/tests cannot be applied, because the repository doesn't have them

In response to this:

What type of PR is this?
/kind cleanup

Any specific area of the project related to this PR?
/area tests

What this PR does / why we need it:

Use testify to assert the test results to make more clean and avoid writing more code

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[cpanato]

testfy catchs a broken test :)

[poiana]

LGTM label has been added.

Git tree hash: a7252c423abc8b33830410c7112a20d013157c4c

[poiana]

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