I can't offer a solution to what it was made with, but the italicization on this paragraph makes me almost sure it was a markdown source. The go tool also su

I can't offer a solution to what it was made with, but the italicization on this paragraph makes me almost sure it was a markdown source. The go tool also supports a special package declaration, ending in test, ie., package http_test. This allows your test files to live alongside your code in the same package, however when those tests are compiled they are not part of your package’s code, they live in their own package. This allows you to write your tests as if you were another package calling into your code. This is known as an _external test.