Port of tests from F# code for 'pickAlternatelyFrom'. I am slightly worried by the fact that two of the tests pass for the obviously incorrect stub implementation - although this might be OK due to the trivial implementation coincidentally having some but not all of the desired properties. I'll check this ...
Checked against F# tests - one of the tests that passes in the previous Scala commit fails in F#, because 'zip' in F# requires the collections to be of equal length as a precondition, so it was doing additional verification. Scala's version of 'zip' simply truncates the output, so the test has been bolstered to fail. The stub implementation has become more realistic, but is still incorrect - wanted to catch the tests out.