Advocate gotestsum for running go test

[afbjorklund]

Since it allows both progress and json, at the same time (not either / or).

It also has a default format that is more friendly on the eyes than go test.

$ gotestsum --jsonfile test_report.json

https://github.com/gotestyourself/gotestsum

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Main issue is recording the current date and execution time "somewhere"...

• #21

Duration (should be the test execution time, not the report execution time)

testExecutionDate (should be the test executation date, not the current date)