Fix and enable CI unit testing for windows

[apostasie]

Reopening erroneously closed previous PR.

This one no longer depends on other pending CI changes and can be merged now.

Take-away:

• couple of tests marked as not compatible
• one test that is blatantly disagreeing with code has been adapted
• error output specialization
• filepath.Join
• enforcing windows-unit on CI

[apostasie]

@djdongjin if you are around - this was previously dependent / blocked by other under-review PRs (eg: part5), but I rebased that differently, and could be merged now.

[djdongjin]

why only windows requires this?

[apostasie]

Magic trick. :-)

[apostasie]

Here is my tentative explanation: somewhere, unit tests do go through a code path that depends on generateNetworkConfig, which is going to check for a binary on the system for the corresponding plugin-type name (GetPluginType).

For windows, it is looking for "nat", which is only provided by the cni plugins.

For linux, it is looking for "bridge"... which is present on most systems and have nothing to do with CNI - hence we get away with running the unit tests.

I do not think the unit tests themselves actually depend on running the binary (obviously...), but yep, that is making the case that we should look into that code.

[AkihiroSuda]

Shouldn't this be os.Getenv("TEMP")

[apostasie]

The path /tmp/oci-layout was / is hardcoded in the oci query part of the test:

nerdctl/pkg/cmd/builder/build_test.go

Lines 206 to 213 in ca76611

	ociLayoutPath: "/tmp/oci-layout/",
	expectedArgs: []string{},
	expectedErr: ErrOCILayoutPrefixNotFound.Error(),
	},
	{
	name: "DirectoryNotFoundError",
	ociLayoutName: "unit-test",
	ociLayoutPath: "oci-layout:///tmp/oci-layout",

We could change it in both the test declaration and the assert - to GetTemp / Getenv (or whatever) else - but I am not sure it would serve much purpose: it seems this test is solely testing the parsing part of parseBuildContextFromOCILayout - which does exactly that (filepath.Abs) after stripping the scheme and will immediately error since there is no oci data in that location.

nerdctl/pkg/cmd/builder/build.go

Line 562 in ca76611

abspath, err := filepath.Abs(path)

The path could very much be /foo/bar for all intent and purpose, and I presume who wrote the test did just put /tmp/oci-layout because that was the first thing they had in mind.

Lmk your thoughts.

[apostasie]

To be completely honest, I am not sure this test is bringing much (or any) value, but then, it is here - so...

[AkihiroSuda]

Thanks