Allow to pass dry_run boolean to lsb_release

So that we consistently return the same value from lsb_release() across
all calls that use dry-run, the function now accepts a dry_run argument
(defaulting to False). This way, in dry-run mode, the caller does not
need to supply the path to a specific example file anymore.

  lsb_release(dry_run=True) -> will load examples/lsb-release-focal

Having said that, the caller is still left with the possibility to
specify the example file by using the path argument:

  lsb_release(path="example/lsb-release-impish")

The path and dry_run arguments are mutually exclusive: providing both
will result in a ValueError.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquitycore/lsb_release.py

@@ -2,13 +2,17 @@
 import shlex
 
 LSB_RELEASE_FILE = "/etc/lsb-release"
+LSB_RELEASE_EXAMPLE = "examples/lsb-release-focal"
 
 
-def lsb_release(path=None):
+def lsb_release(path=None, dry_run: bool = False):
     """return a dictionary of values from /etc/lsb-release.
     keys are lower case with DISTRIB_ prefix removed."""
+    if dry_run and path is not None:
+        raise ValueError("Both dry_run and path are specified.")
+
     if path is None:
-        path = LSB_RELEASE_FILE
+        path = LSB_RELEASE_EXAMPLE if dry_run else LSB_RELEASE_FILE
 
     ret = {}
     try:

subiquitycore/tests/test_lsb_release.py

@@ -0,0 +1,58 @@
+# Copyright 2021 Canonical, Ltd.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+from unittest.mock import patch, mock_open
+
+from subiquitycore.lsb_release import lsb_release
+
+
+class TestLSBRelease(unittest.TestCase):
+    def setUp(self):
+        self.target = "subiquitycore.lsb_release.open"
+
+    def test_lsb_release(self):
+        lsb_str = """
+DISTRIB_ID=Ubuntu
+DISTRIB_RELEASE=21.10
+DISTRIB_CODENAME=impish
+DISTRIB_DESCRIPTION="Ubuntu 21.10"
+        """
+
+        with patch(self.target, mock_open(read_data=lsb_str)) as patched:
+            distro = lsb_release(path="dummy")
+            patched.assert_called_once_with("dummy", "r")
+            self.assertEqual(distro["id"], "Ubuntu")
+            self.assertEqual(distro["release"], "21.10")
+            self.assertEqual(distro["codename"], "impish")
+            self.assertEqual(distro["description"], "Ubuntu 21.10")
+
+    def test_lsb_release_inexistent(self):
+        with patch(self.target, side_effect=FileNotFoundError):
+            self.assertEqual(lsb_release("/inexistent"), {})
+
+    def test_lsb_release_default(self):
+        with patch(self.target, side_effect=FileNotFoundError) as patched:
+            lsb_release(path=None)
+            patched.assert_called_once_with("/etc/lsb-release", "r")
+
+    def test_lsb_release_dry_run(self):
+        with patch(self.target, side_effect=FileNotFoundError) as patched:
+            lsb_release(dry_run=True)
+            patched.assert_called_once_with("examples/lsb-release-focal", "r")
+
+    def test_lsb_release_mutually_exclusive(self):
+        with self.assertRaises(ValueError):
+            lsb_release(path="dummy", dry_run=True)