Per the documentation, I tried copying existing files in testdata/config1 and testdata/config2 to testdata/fuzz/Decode. This failed because I should have put them in testdata/fuzz/FuzzDecode but that (repetition of the word "fuzz") wasn't obvious to me from the docs.
I then tried running the fuzzer on Go tip (629ffeb) and got:
--- FAIL: FuzzDecode (0.00s)
fuzz_test.go:9: "testdata/fuzz/FuzzDecode/config1": unmarshal: unknown encoding version: Host localhost 127.0.0.1 # A comment at the end of a host line.
"testdata/fuzz/FuzzDecode/config2": unmarshal: unknown encoding version: # $OpenBSD: ssh_config,v 1.30 2016/02/20 23:06:23 sobrado Exp $
I'm not sure how to resolve that. The docs that I saw (the blog post and in src/testing/testing.go) didn't mention anything about a version format for seed files, and the error message does not explain how to resolve the issue.
I also tried searching Google for information if other people had run into the error, and didn't find any.