subp: add 'update_env' argument

In order for a caller to use 'env' argument of subp, they
will realistically do:
  env = os.environ.copy()
  env['FOO'] = 'BZR'
  subp(cmd, env=env)

This shortens that to be:
  subp(cmd, update_env={'FOO': 'BZR'})

Add tests, and update growpart tests to use mock when playing with
os.environ.

1 files changed, 28 insertions, 2 deletions

diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index d2031f59..30f603cb 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -223,8 +223,10 @@ class TestKeyValStrings(helpers.TestCase):
 
 class TestGetCmdline(helpers.TestCase):
     def test_cmdline_reads_debug_env(self):
-        os.environ['DEBUG_PROC_CMDLINE'] = 'abcd 123'
-        self.assertEqual(os.environ['DEBUG_PROC_CMDLINE'], util.get_cmdline())
+        with mock.patch.dict("os.environ",
+                             values={'DEBUG_PROC_CMDLINE': 'abcd 123'}):
+            ret = util.get_cmdline()
+        self.assertEqual("abcd 123", ret)
 
 
 class TestLoadYaml(helpers.TestCase):
@@ -516,6 +518,7 @@ class TestSubp(helpers.TestCase):
     utf8_invalid = b'ab\xaadef'
     utf8_valid = b'start \xc3\xa9 end'
     utf8_valid_2 = b'd\xc3\xa9j\xc8\xa7'
+    printenv = ['bash', '-c', 'for n in "$@"; do echo "$n=${!n}"; done', '--']
 
     def printf_cmd(self, *args):
         # bash's printf supports \xaa.  So does /usr/bin/printf
@@ -566,6 +569,29 @@ class TestSubp(helpers.TestCase):
         self.assertEqual(err, data)
         self.assertEqual(out, b'')
 
+    def test_subp_reads_env(self):
+        with mock.patch.dict("os.environ", values={'FOO': 'BAR'}):
+            out, err = util.subp(self.printenv + ['FOO'], capture=True)
+        self.assertEqual('FOO=BAR', out.splitlines()[0])
+
+    def test_subp_env_and_update_env(self):
+        out, err = util.subp(
+            self.printenv + ['FOO', 'HOME', 'K1', 'K2'], capture=True,
+            env={'FOO': 'BAR'},
+            update_env={'HOME': '/myhome', 'K2': 'V2'})
+        self.assertEqual(
+            ['FOO=BAR', 'HOME=/myhome', 'K1=', 'K2=V2'], out.splitlines())
+
+    def test_subp_update_env(self):
+        extra = {'FOO': 'BAR', 'HOME': '/root', 'K1': 'V1'}
+        with mock.patch.dict("os.environ", values=extra):
+            out, err = util.subp(
+                self.printenv + ['FOO', 'HOME', 'K1', 'K2'], capture=True,
+                update_env={'HOME': '/myhome', 'K2': 'V2'})
+
+        self.assertEqual(
+            ['FOO=BAR', 'HOME=/myhome', 'K1=V1', 'K2=V2'], out.splitlines())
+
     def test_returns_none_if_no_capture(self):
         (out, err) = util.subp(self.stdin2out, data=b'', capture=False)
         self.assertEqual(err, None)