Do not ignore Union argument ordering in tests

[dairiki]

The union argument ordering is important!

What's here:

• Revert b61cd5035b7ec0722e1ac7a361cbd9e8f6a4387a. That commit effectively hides failing tests by ignoring the argument order of union fields.
• The one test that fails because of that reversion is marked an expected failure.
• A new version of that failing test is added. The new version does ignore the union argument ordering (and so is expected to pass).

Related

The failing test fails due to #247.

This was discussed in PR #246.