tests: improve tests that are supposed to throw

[weissi]

Motivation:

The

do {
    try someOperation()
XCTFail("should throw") // easy to forget
} catch error as SomethingError {
    XCTAssertEqual(.something, error as? SomethingError)
} catch {
    XCTFail("wrong error")
}

pattern is not only very long, it's also very error prone. If you forget
any of the XCTFails, you might not tests what it looks like

XCTAssertThrowsError(try someOperation) { error in
    XCTAssertEqual(.something, error as? SomethingError)
}

is much safer and shorter.

Modifcations:

Do many of the above replaces.

Result:

Cleaner, shorter, and safer tests.

[glbrntt]

Is there any value in something like assertMaybeThrows which validates the error if one is thrown but doesn't fail if no error is thrown? I think I've only seen one or two occurrences of this elsewhere here so probably not...

[weissi]

There are a few but unfortunately our TestUtils.swift doesn't really scale. It's always just available in one test module but we have lots of modules and like 5 different repos :|. So I now prefer to stick with plain XCTest whenever possible...