Marshall core unit tests

[a-ivanov]

First-time contributor here!

Added unit tests for core functions from marshalls.h as discussed in #43440.
Haven't created ones for encode/decode Variant functions yet. In process of creating tests for different cases of Variant types.

Thanks.

[a-ivanov]

Ah, has just noticed the requirement about intermediate commits.
Do I need to squash current commits into one?

Also, if I plan to add Variant related tests, should I squash it too? Or should I create a new PR with Variant tests in separate commit?

[akien-mga]

Ah, has just noticed the requirement about intermediate commits.
Do I need to squash current commits into one?

Indeed, that would be good. See PR workflow for instructions.

Also, if I plan to add Variant related tests, should I squash it too? Or should I create a new PR with Variant tests in separate commit?

If it's tests which should be part of the Marshall unit tests, they should likely be in this PR too. Could be a separate commit, or squash into the original one, depending on how "separate" they are in scope and implementation.

[aaronfranke]

Since we are testing the validity of an encoded value, this should be exact equality, not approximate equality.

Also, you don't need to use the exact decimal value for the literal. Any decimal literal will automatically become the closest possible double, so we just need to put enough threes (17 digits is the safe amount) for it to become 0.333333333333333314829616256247390992939472198486328125.

Suggested change

	CHECK(Math::is_equal_approx(decode_double(arr), 0.333333333333333314829616256247390992939472198486328125));
	CHECK(decode_double(arr) == 0.33333333333333333));

[a-ivanov]

I agree, done.

[aaronfranke]

Looks good to me. Someone else should also review this though.

[Xrayez]

Looks good enough to me!

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[a-ivanov]

Actually it was an interesting dig to become more familiar with the engine.