mime: TestExtensionsByTypeMultiple broken on windows

[cookieo9]

On my windows machine (Windows 8.1 64-bit), the TestExtensionsByTypeMultiple test breaks consistently with the following error at tip:

--- FAIL: TestExtensionsByTypeMultiple (0.00s)
        type_test.go:76: ExtensionsByType("text/html") = [.htm .html .shtml]; want [.htm .html]

This is likely the result of the MIME types map being made using data from the registry, and my system having an extra entry for text/html that the test wasn't expecting.

I did not add the entry manually myself, so it's either a default for my version of the OS (compared to the builder's) or an addition made by a program I installed. Either case, the test should be probably be made more robust, or ignore the registry's mime-entries during testing.

[bradfitz]

Thanks.

These tests need to be more insulated. They're testing too many unrelated things at once. The types_test.go tests are mixing testing the various functions and also testing parsing the OS-specific text files. Those need to be separate tests, and tests like TestExtensionsByTypeMultiple need to be testing just those functions on static data baked into the tests and not let OS-specific differences creep in.

[bradfitz]

I sent: https://go-review.googlesource.com/8213