T011

A new test kills none of the mutants of the changed lines: it would still pass if that code were wrong (a warning when the mutants were sampled).

Fix: Assert what the changed code computes; the gate's surviving mutants say what to check.

Status in weft@0.1.0: reported by weft test --gate on a diff.

A test that needs it on purpose keeps it with a reason: // weft-allow T011: <why> in the file header (whole file) or on the line above.