Tests: prerequisites checking reworked.

Prerequisites check moved to the module level to simplify class structure.
Discovery and prerequisites checks functions moved to the separate files.
Introduced "require" fixture to provide per-test requirements check.

test/test_python_isolation.py

@@ -10,10 +10,10 @@ from unit.utils import findmnt
 from unit.utils import waitformount
 from unit.utils import waitforunmount
 
+prerequisites = {'modules': {'python': 'any'}, 'features': {'isolation': True}}
+
 
 class TestPythonIsolation(TestApplicationPython):
-    prerequisites = {'modules': {'python': 'any'}, 'features': ['isolation']}
-
     def get_cgroup(self, app_name):
         output = subprocess.check_output(
             ['ps', 'ax', '-o', 'pid', '-o', 'cmd']
@@ -31,25 +31,23 @@ class TestPythonIsolation(TestApplicationPython):
         with open(cgroup, 'r') as f:
             return f.read().rstrip()
 
-    def test_python_isolation_rootfs(self, is_su, temp_dir):
-        isolation_features = option.available['features']['isolation'].keys()
-
-        if not is_su:
-            if not 'unprivileged_userns_clone' in isolation_features:
-                pytest.skip('requires unprivileged userns or root')
-
-            if 'user' not in isolation_features:
-                pytest.skip('user namespace is not supported')
-
-            if 'mnt' not in isolation_features:
-                pytest.skip('mnt namespace is not supported')
-
-            if 'pid' not in isolation_features:
-                pytest.skip('pid namespace is not supported')
-
+    def test_python_isolation_rootfs(self, is_su, require, temp_dir):
         isolation = {'rootfs': temp_dir}
 
         if not is_su:
+            require(
+                {
+                    'features': {
+                        'isolation': [
+                            'unprivileged_userns_clone',
+                            'user',
+                            'mnt',
+                            'pid',
+                        ]
+                    }
+                }
+            )
+
             isolation['namespaces'] = {
                 'mount': True,
                 'credential': True,
@@ -78,9 +76,8 @@ class TestPythonIsolation(TestApplicationPython):
 
         assert ret['body']['FileExists'], 'application exists in rootfs'
 
-    def test_python_isolation_rootfs_no_language_deps(self, is_su, temp_dir):
-        if not is_su:
-            pytest.skip('requires root')
+    def test_python_isolation_rootfs_no_language_deps(self, require, temp_dir):
+        require({'privileged_user': True})
 
         isolation = {'rootfs': temp_dir, 'automount': {'language_deps': False}}
         self.load('empty', isolation=isolation)
@@ -103,9 +100,8 @@ class TestPythonIsolation(TestApplicationPython):
 
         assert waitforunmount(python_path), 'language_deps unmount'
 
-    def test_python_isolation_procfs(self, is_su, temp_dir):
-        if not is_su:
-            pytest.skip('requires root')
+    def test_python_isolation_procfs(self, require, temp_dir):
+        require({'privileged_user': True})
 
         isolation = {'rootfs': temp_dir, 'automount': {'procfs': False}}
 
@@ -123,12 +119,10 @@ class TestPythonIsolation(TestApplicationPython):
             'FileExists'
         ], '/proc/self'
 
-    def test_python_isolation_cgroup(self, is_su):
-        if not is_su:
-            pytest.skip('requires root')
-
-        if not 'cgroup' in option.available['features']['isolation']:
-            pytest.skip('cgroup is not supported')
+    def test_python_isolation_cgroup(self, require):
+        require(
+            {'privileged_user': True, 'features': {'isolation': ['cgroup']}}
+        )
 
         def set_cgroup_path(path):
             isolation = {'cgroup': {'path': path}}
@@ -146,12 +140,10 @@ class TestPythonIsolation(TestApplicationPython):
 
         assert len(cgroup_rel.parts) >= len(cgroup_abs.parts)
 
-    def test_python_isolation_cgroup_two(self, is_su):
-        if not is_su:
-            pytest.skip('requires root')
-
-        if not 'cgroup' in option.available['features']['isolation']:
-            pytest.skip('cgroup is not supported')
+    def test_python_isolation_cgroup_two(self, require):
+        require(
+            {'privileged_user': True, 'features': {'isolation': ['cgroup']}}
+        )
 
         def set_two_cgroup_path(path, path2):
             script_path = f'{option.test_dir}/python/empty'
@@ -193,12 +185,10 @@ class TestPythonIsolation(TestApplicationPython):
         set_two_cgroup_path('/scope/python', '/scope2/python')
         assert self.get_cgroup('one') != self.get_cgroup('two')
 
-    def test_python_isolation_cgroup_invalid(self, is_su):
-        if not is_su:
-            pytest.skip('requires root')
-
-        if not 'cgroup' in option.available['features']['isolation']:
-            pytest.skip('cgroup is not supported')
+    def test_python_isolation_cgroup_invalid(self, require):
+        require(
+            {'privileged_user': True, 'features': {'isolation': ['cgroup']}}
+        )
 
         def check_invalid(path):
             script_path = f'{option.test_dir}/python/empty'