replace ==, !=, some instances of var, and assert.equal()

Checklist

• make -j8 test (UNIX), or vcbuild test nosign (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

tests

Description of change

• replaced == with ===
• replaced != with !==
• replaced some var instances with const
• replaced assert.equal() with assert.strictEqual()