test: add test for chroot context

Add a test for the chroot context that mocks subprocess.run() and
subprocess.check_call().  The test verifies that the functions are
called the expected number of times with the expected command (first
arg).

test/mod/test_util_chroot.py

@@ -0,0 +1,34 @@
+#
+# Test for util/chroot.py
+#
+
+from unittest.mock import patch
+
+from osbuild.util.chroot import Chroot
+
+
+class RunReturn:
+    """
+    Class to be returned from mocked run() call so that the returncode is always 0.
+    """
+
+    @property
+    def returncode(self):
+        return 0
+
+
+@patch("subprocess.check_call")
+@patch("subprocess.run", return_value=RunReturn())
+def test_chroot_context(mocked_run, mocked_check_call):
+
+    with Chroot("") as chroot:  # the path doesn't matter since nothing is actually running
+        chroot.run(["/bin/true"])
+
+    assert mocked_run.call_count == 4  # the chroot.run() call + 3 umount calls
+    assert mocked_run.call_args_list[0].args[0][0] == "/usr/sbin/chroot"
+    for call_run in mocked_run.call_args_list[1:]:
+        assert call_run.args[0][0] == "/usr/bin/umount"
+
+    assert mocked_check_call.call_count == 3  # 3 mount calls
+    for check_run in mocked_check_call.call_args_list:
+        assert check_run.args[0][0] == "/usr/bin/mount"