Tests should should modify flatpak manifest to pull the HEAD commit

[andyholmes]

I noticed while working on #83 that (in the case of git, for example) flatpak-builder will build from the sources defined in the flatpak manifest. This isn't surprising, but it's almost certainly not what you want if your manifest points to your main branch and you are running tests on pull request.

I plan on taking a crack at this eventually, but if someone else wants to take it on before I do, feel free.

[bilelmoussaoui]

We already do that no? What is the flatpak manifest you are using? because we expect people to use a type: dir in their manifest instead of a type: git

[andyholmes]

Ah, I see! I've been using basically a copy of a manifest I use to build nightly bundles, with some minor changes such as -Dtests=true.

Would you accept a PR to add some documentation for this, to close this issue? From looking at some manifests, I'm guessing that that path: ... in the type: dir sources is relative to the manifest's location to the project root? For example:

/build-aux/flatpak/app.foo.Bar.json     => "path": "../../"
/deeper/path/structure/app.foo.Bar.json => "path": "../../../"

Is that right?