Build/Test Tools: Replace some instances of `assertEquals()`.
This PR replaces assertEquals() with more appropriate, stricter assertions where possible and without making any changes to source.
For easier reviewing, commits have been separated based on the replacement assertion and any additional changes required to implement the stricter assertion.
Trac ticket: https://core.trac.wordpress.org/ticket/63169 Trac ticket: https://core.trac.wordpress.org/ticket/62278 Trac ticket: https://core.trac.wordpress.org/ticket/61573 Trac ticket: https://core.trac.wordpress.org/ticket/60706 Trac ticket: https://core.trac.wordpress.org/ticket/59655 Trac ticket: https://core.trac.wordpress.org/ticket/55654 Trac ticket: https://core.trac.wordpress.org/ticket/54726 Track ticket: https://core.trac.wordpress.org/ticket/63169