Add test cases for Hash#asset_valid_keys

I don't think the others (checking for a single name where we're already checking for two) are worthwhile. But please do update to contain just these two `:sunny` ones... and fix them to use `:failure` instead of `:failore` (which is only used elsewhere when a mismatch is intended).

Actually, can you move these two into a separate `assert_nothing_raised` block, with a leading comment `# not all valid keys are required to be present`?