Fix "Mocha methods cannot be used outside the context of a test"

Calling some test functions outside of test blocks seems to now fail tests.

See all of the recent puppet-test-full-STEAM jobs:

An error occurred while loading ./spec/unit/provider/jks_spec.rb.
Failure/Error: File.any_instance.stubs(:file?).returns(true)

Mocha::NotInitializedError:
Mocha methods cannot be used outside the context of a test

1. ./spec/unit/provider/jks_spec.rb:6:in `<top (required)>'

Deprecation Warnings:

puppetlabs_spec_helper: defaults `mock_with` to `:mocha`. See https://github.com/puppetlabs/puppetlabs_spec_helper#mock_with to choose a sensible value for you

https://logs.opendaylight.org/releng/vex-yul-odl-jenkins-1/puppet-test-full-master/405/console.log.gz