Improving reliability of get_current_url tests

[pauarge]

Description

This PR improves the tests on the get_current_url function. Concretely, we're changing how we check the results, from assertStringStartsWith to the stricter assertEquals.

With this PR, we have tests to prove that if a query parameter, such as ?p=1 gets added to the URL, the function will correctly catch it. This closes an issue (linked below) that pointed to this function not working correctly.

Motivation and Context

#151

How Has This Been Tested?

Ran PHPUnit tests locally and in CI.

Types of changes

New feature (non-breaking change which adds functionality)

[GaryJones]

The focus of these tests is on the parsing issues related to the domain, port, and potential path, and this is represented in the data provider.

However, it's good to be able to confirm that going to the homepage, random URL and a post via its ID, also work well for each of the combinations in the first parts of the URL.

Since the setup is the same for each of the tests, we can just merge these three tests into one, and have it test the homepage, a specific post, and a random URL, and add the message attribute to the assertions to make it clear which part might have failed.

If you're happy with my changes @pauarge, then I can rebase into a single commit or it can be merged with a squash, to keep the history cleaner.

[pauarge]

@GaryJones Your changes look good to me, they make the tests easier to read. It's a 👍 from my side.