Force test report encoding to UTF-8.

[fonglh]

Originally ASCII-8BIT which causes problems for to_json later in the
Flexirest gem.

Fixes #59, fixes #58.

[fonglh]

How should I test this?

[houndci-bot]

Freezing immutable objects is pointless.

[allenwq]

Can you add ASCII-8BIT characters and test ? hard to tell it works or not.

[fonglh]

It's the same byte sequence, just that the encoding attached to the string is different.

[allenwq]

But why not add invalid characters to the template and test ? That will enforce all later changes works with those characters.

[fonglh]

There are no existing tests that will trigger this bug, even if non ASCII characters are added to the test fixtures.

That's because the exception happens during the .to_json conversion in the flexirest gem, when the save endpoint is called. The existing tests stub save, and the existing tests for the programming evaluation service won't crash even with ASCII-8BIT encoding.

An end-to-end test is needed, but this is actually a test of flexirest, rather than the evaluator gem.