tests: fix test_group_filter_imports()

Fixing the test case logic causes it to fail, so mark it xfail.
This is bug zephyrproject-rtos#663.

The test case test_group_filter_self_import() is incorrect, which
conveniently enough provides steps to reproduce.

The test case should read as follows (patch applies to f6f5cf6):

diff --git a/tests/test_manifest.py b/tests/test_manifest.py
index 14f2941..e934b71 100644
--- a/tests/test_manifest.py
+++ b/tests/test_manifest.py
@@ -2828,7 +2828,7 @@ def test_group_filter_imports(manifest_repo):
     sha2 = setup_project('project2', '[+gy,+gy,-gz]')

     v0_9_expected = ['+ga', '-gc']
-    v0_10_expected = ['-ga', '-gb', '-gc', '-gw', '-gy', '-gz']
+    v0_10_expected = ['-ga', '-gb', '-gc', '-gw', '-gz']

     #
     # Basic tests of the above setup.

In other words, west incorrectly concludes that group 'gy' is disabled
in this scenario, when it should be enabled.

The test creates the following layout, where ./mp/west.yml is the main
manifest:

    ───────────────────────────────────────
     File: ./mp/west.yml
    ───────────────────────────────────────
     manifest:
       version: "0.10"

       group-filter: [+ga,-gc]

       projects:
         - name: project1
           revision: ...
           import: true
         - name: project2
           revision: ...
           import: true

       self:
         import: self-import.yml
    ..
    ───────────────────────────────────────

    ───────────────────────────────────────
     File: ./project1/west.yml
    ───────────────────────────────────────
     manifest:
       group-filter: [-gw,-gw,+gx,-gy]
    ───────────────────────────────────────

    ───────────────────────────────────────
     File: ./project2/west.yml
    ───────────────────────────────────────
     manifest:
       group-filter: [+gy,+gy,-gz]
    ───────────────────────────────────────

    ───────────────────────────────────────
     File: ./mp/self-import.yml
    ───────────────────────────────────────
     manifest:
       group-filter: [-ga,-gb]
    ───────────────────────────────────────

The west docs say:

  In other words, let:

  - the submanifest resolved from self-import have group filter self-filter
  - the top-level manifest file have group filter top-filter
  - the submanifests resolved from import-1 through import-N have
    group filters filter-1 through filter-N respectively

  The final resolved group-filter value is then filter1 + filter-2 +
  ... + filter-N + top-filter + self-filter, where + here refers to
  list concatenation.

  - https://docs.zephyrproject.org/latest/develop/west/manifest.html

Applying these rules, the final filter should be concatenated from
./project1/west.yml, ./project2/west.yml, ./mp/west.yml,
./mp/self-import.yml, in that order. Since neither ./mp/west.yml nor
./mp/self-import.yml have a group filter which affects gy, the result
should be that it is enabled, since ./project2/west.yml enables it
explicitly.

Fix the test so it matches the expected behavior. We'll fix the
implementation in a separate commit.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

tests/test_manifest.py

@@ -2770,6 +2770,7 @@ def self_import_helper(manifest_version_line, expected_group_filter):
     self_import_helper('', [])
     self_import_helper('version: 0.9', ['-foo'])
 
+@pytest.mark.xfail
 def test_group_filter_imports(manifest_repo):
     # More complex test that ensures group filters are imported correctly:
     #
@@ -2827,7 +2828,7 @@ def setup_project(name, group_filter):
     sha2 = setup_project('project2', '[+gy,+gy,-gz]')
 
     v0_9_expected = ['+ga', '-gc']
-    v0_10_expected = ['-ga', '-gb', '-gc', '-gw', '-gy', '-gz']
+    v0_10_expected = ['-ga', '-gb', '-gc', '-gw', '-gz']
 
     #
     # Basic tests of the above setup.