Gracefully accept the pluralization “1 generators” in test output

[wilfwilson]

As well as comparing the expected and obtained test outputs up to whitespace, we now also consider "1 generator" and "1 generators" to be equivalent. This resolves #71.

The strategy is not completely bulletproof, since it would also consider "21 generators" and "21 generator" to be equivalent, but this should not occur, and even if it does, it only makes it easier to introduce a grammatical error (in pluralisation), not a mathematical error.

[codecov[bot]]

Codecov Report

Merging #72 (9dab5a4) into master (a460fda) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #72   +/-   ##
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  Coverage   59.82%   59.82%           
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  Files          74       74           
  Lines       22724    22724           
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  Hits        13594    13594           
  Misses       9130     9130           

[fingolfin]

Looks good to me, I hope @sunnyquiver agrees