Are Characterization (Golden Master/Snapshot) tests supposed to be human readable?

Generally, characterisation tests are not an end state. They're a way to pin the current behaviour of untested legacy code, so that you can start making changes towards maintainability and testability with a reasonable level of confidence that the overall picture hasn't changed. They're not good tests, though, they don't:

• tell you any of the behaviour is actually correct;

• tell you where the problem is when a test starts failing (they're just detecting changes); or

• tell you which parts of the current implementation are important.

So readability isn't particularly important in this case; once you have explored the behaviour more thoroughly, found the overlaps between the test cases (and which ones shouldn't have passed) and written higher quality tests that give you real confidence, you can get rid of most if not all of them.

The other use for characterisation tests is where the alternatives would be less readable, e.g. when you have code that outputs a report and you don't want to have to exhaustively check each part of it. Instead you generate the report, manually check it and then compare future reports to it to make sure nothing changes. Although this "snapshot"-style testing can be harmful at lower levels, enforcing "change detection" that actually prevents refactoring, at this level it's useful.