After opts, this is another big one — probably a little too big.. It's the time for runconfig to get covered 🐸.

What this PR does is :

• A small re-organization of existing tests (putting the parsing one into parse_test.go, the merging one into merge_test.go, and so on).
• Add compare_test.go for more extensive testing of the Compare config method.
• Update config_test.go to test Entrypoint and Command structs (that might be overkill but… oh well 😺).
• Add exec_test.go to test ParseExec (which is in exec.go).
• Add hostconfig_test.go for hostconfig.go tests, with fixtures (similar to what was done with config_test.go).
• Update parse_test.go to cover more cases. As some of some parse thingy are calling the opts package and some aren't I tried to limit test case for those shared validation cases. I'll use the data gathered by those PR to update the issue I created about the need to centralize some of the checks (Proposal : centralize validations / checks between cli, api & builder #13824).

There is a few FIXME in there, question I was asking myself and not really able to answer. I'll comment on them directly in this PR.

# Before
+ go test -test.timeout=30m github.com/docker/docker/runconfig
PASS
coverage: 54.6% of statements
# After
+ go test -test.timeout=30m github.com/docker/docker/runconfig
PASS
coverage: 94.8% of statements

It's probably gonna be a little tricky to merge, because some PRs might changes these files a bit (like #14133) — but I'll rebase, fix or remove tests if needed (or even split this PR into severals).

Thanks for the reviews :)

Signed-off-by: Vincent Demeester vincent@sbr.pm