test: move stage-tests into test/run and test/data

Move the stage-tests over to the new test-infrastructure. This moves
the test invocation into `./test/run/test_stages.py`, so it is invoked
as part of the runtime-tests. Secondly, the test-data is stored in
./test/data/stages/ so the path is relative to
TestBase.locate_test_data().

While at it, this also drops the dynamic class modifications and instead
uses subTest(). This simplifies the code quite a bit and avoids
dynamically creating python code.

.github/workflows/runtime-tests.yml

@@ -46,25 +46,3 @@ jobs:
       run: pip install jsonschema
     - name: "Run Assembler Tests"
       run: sudo env "PATH=$PATH" python3 -m unittest -v test.test_assemblers
-
-  stage_tests:
-    name: "Stage Tests"
-    runs-on: ubuntu-latest
-    steps:
-    - name: "Clone Repository"
-      uses: actions/checkout@v2
-    - name: "Install Dependencies"
-      run: |
-        sudo apt-get update
-        sudo apt-get -y install \
-          systemd-container \
-          tar \
-          yum
-    - name: "Set up Python"
-      uses: actions/setup-python@v1
-      with:
-        python-version: 3.7
-    - name: Install Python Packages
-      run: pip install jsonschema
-    - name: "Run Stage Tests"
-      run: sudo env "PATH=$PATH" python3 -m unittest -v test.test_stages

test/run/test_stages.py

@@ -1,3 +1,7 @@
+#
+# Runtime tests for the individual stages.
+#
+
 import difflib
 import json
 import os
@@ -5,10 +9,12 @@ import pprint
 import tempfile
 import unittest
 
-from . import test
+from .. import test
 
 
-class TestDescriptions(test.TestBase):
+@unittest.skipUnless(test.TestBase.have_test_data(), "no test-data access")
+@unittest.skipUnless(test.TestBase.have_tree_diff(), "tree-diff missing")
+class TestStages(test.TestBase):
 
     def assertTreeDiffsEqual(self, tree_diff1, tree_diff2):
         """
@@ -113,19 +119,8 @@ class TestDescriptions(test.TestBase):
 
             self.assertTreeDiffsEqual(expected_diff, actual_diff)
 
-
-def generate_test_case(path):
-    @unittest.skipUnless(test.TestBase.have_tree_diff(), "tree-diff missing")
-    def test_case(self):
-        self.run_stage_test(path)
-
-    return test_case
-
-
-def init_tests():
-    test_dir = 'test/stages_tests'
-    for name in os.listdir(test_dir):
-        setattr(TestDescriptions, f"test_{name}", generate_test_case(f"{test_dir}/{name}"))
-
-
-init_tests()
+    def test_stages(self):
+        path = os.path.join(self.locate_test_data(), "stages")
+        for name in os.listdir(path):
+            with self.subTest(stage=name):
+                self.run_stage_test(os.path.join(path, name))