test: convert to shared helpers

Use the `can_modify_immutable()` helper from the TestBase parent class
so we do not duplicate the code in multiple places. Similarly, make use
of the `have_rpm_ostree()` helper.

test/mod/test_util_linux.py

@@ -9,18 +9,7 @@ import unittest
 
 from osbuild.util import linux
 
-
-def can_set_immutable():
-    with tempfile.TemporaryDirectory(dir="/var/tmp") as tmp:
-        try:
-            os.makedirs(f"{tmp}/f")
-            # fist they give it ...
-            subprocess.run(["chattr", "+i", f"{tmp}/f"], check=True)
-            # ... then they take it away
-            subprocess.run(["chattr", "-i", f"{tmp}/f"], check=True)
-        except (subprocess.CalledProcessError, FileNotFoundError):
-            return False
-        return True
+from .. import test
 
 
 class TestUtilLinux(unittest.TestCase):
@@ -30,6 +19,7 @@ class TestUtilLinux(unittest.TestCase):
     def tearDown(self):
         self.vartmpdir.cleanup()
 
+    @unittest.skipUnless(test.TestBase.can_modify_immutable("/var/tmp"), "root-only")
     def test_ioctl_get_immutable(self):
         #
         # Test the `ioctl_get_immutable()` helper and make sure it works
@@ -39,7 +29,7 @@ class TestUtilLinux(unittest.TestCase):
         with open(f"{self.vartmpdir.name}/immutable", "x") as f:
             assert not linux.ioctl_get_immutable(f.fileno())
 
-    @unittest.skipUnless(can_set_immutable(), "root-only")
+    @unittest.skipUnless(test.TestBase.can_modify_immutable("/var/tmp"), "root-only")
     def test_ioctl_toggle_immutable(self):
         #
         # Test the `ioctl_toggle_immutable()` helper and make sure it works

test/mod/test_util_ostree.py

@@ -8,6 +8,8 @@ import subprocess
 
 from osbuild.util import ostree
 
+from .. import test
+
 
 def run(*args, check=True, encoding="utf-8", **kwargs):
     res = subprocess.run(*args,
@@ -17,19 +19,10 @@ def run(*args, check=True, encoding="utf-8", **kwargs):
     return res
 
 
-def have_rpm_ostree():
-    try:
-        r = run(["rpm-ostree", "--version"],
-                capture_output=True, check=False)
-    except FileNotFoundError:
-        return False
-    return r.returncode == 0 and "compose" in r.stdout
-
-
 class TestObjectStore(unittest.TestCase):
 
     # pylint: disable=no-self-use
-    @unittest.skipIf(not have_rpm_ostree(), "rpm-ostree missing")
+    @unittest.skipUnless(test.TestBase.have_rpm_ostree(), "rpm-ostree missing")
     def test_treefile_empty(self):
         # check we produce a valid treefile from an empty object
         tf = ostree.Treefile()
@@ -64,7 +57,7 @@ class TestObjectStore(unittest.TestCase):
                 self.assertEqual(js["ref"], test_ref)
                 self.assertEqual(tf["ref"], test_ref)
 
-    @unittest.skipIf(not have_rpm_ostree(), "rpm-ostree missing")
+    @unittest.skipUnless(test.TestBase.have_rpm_ostree(), "rpm-ostree missing")
     def test_treefile_full(self):
         params = {
             "ref": "osbuild/ostree/devel",

test/mod/test_util_rmrf.py

@@ -11,22 +11,11 @@ import unittest
 
 from osbuild.util import rmrf
 
-
-def can_set_immutable():
-    with tempfile.TemporaryDirectory(dir="/var/tmp") as tmp:
-        try:
-            os.makedirs(f"{tmp}/f")
-            # fist they give it ...
-            subprocess.run(["chattr", "+i", f"{tmp}/f"], check=True)
-            # ... then they take it away
-            subprocess.run(["chattr", "-i", f"{tmp}/f"], check=True)
-        except (subprocess.CalledProcessError, FileNotFoundError):
-            return False
-        return True
+from .. import test
 
 
 class TestUtilLinux(unittest.TestCase):
-    @unittest.skipUnless(can_set_immutable(), "Need root permissions")
+    @unittest.skipUnless(test.TestBase.can_modify_immutable("/var/tmp"), "root-only")
     def test_rmtree_immutable(self):
         #
         # Test the `rmrf.rmtree()` helper and verify it can correctly unlink