I'm in agreement he should use more test cases, but it looks like he used the same as Golang's compression tests [1]. Note he has other test cases in the subdirectories (also the same as Go) [2].

However I believe even better testing would be to fuzz it for a few hours [3].

[1] http://golang.org/src/compress/testdata/

[2] https://github.com/klauspost/compress/tree/master/zip/testda...

[3] https://github.com/dvyukov/go-fuzz