Add `execute` function (gd_diff.py).

* gd_diff.py (execute): New function.
* tests/test_gd_diff.py (test_execute_success, test_execute_cmderror)
  (test_execute_raise_exception): Tests for `execute` function.

2 files changed, 46 insertions, 0 deletions

diff --git a/gd_diff.py b/gd_diff.py
index 97cf175..3c704e9 100644
--- a/gd_diff.py
+++ b/gd_diff.py
@@ -6,8 +6,12 @@
 #  gns-deb-diff is under the Public Domain. See
 #  <https://creativecommons.org/publicdomain/zero/1.0>
 
+import shlex
 import sys
 
+from subprocess import run, PIPE
+
+
 # list of recognized fields.
 field_list = [
     "Change-Type",
@@ -28,6 +32,23 @@ def read_file(fpath):
     return f.read()
 
 
+def execute(cmd, out=None, err=None):
+    """Run `cmd`. Returns an instance of `subprocess.CompletedProcess`
+
+    `cmd` must be a string containing the command to run.
+    """
+    cmd = shlex.split(cmd)
+
+    try:
+        completed_process = run(cmd, stdout=out, stderr=err)
+    except (FileNotFoundError, OSError, ValueError) as e:
+        print("Error running '%s'\n Error Info:\n %r" % (cmd[0], e),
+              file=sys.stderr)
+        sys.exit(1)
+
+    return completed_process
+
+
 def get_packages(pkgs_file):
     """Return an iterator contaning of package names from `pkgs_file`.
 
diff --git a/tests/test_gd_diff.py b/tests/test_gd_diff.py
index 650094f..2d6fe86 100644
--- a/tests/test_gd_diff.py
+++ b/tests/test_gd_diff.py
@@ -7,12 +7,14 @@
 #  <https://creativecommons.org/publicdomain/zero/1.0>
 
 import os
+import subprocess
 import sys
 
 from nose.tools import *
 
 from gd_diff import *
 
+
 class TestGdDiff(object):
 
     def setup(self):
@@ -32,6 +34,29 @@ class TestGdDiff(object):
             f_content = read_file(self.pkgs_file_ne)
 
 
+    def test_execute_success(self):
+        cmd = 'python --version'
+        cp = execute(cmd, out=subprocess.PIPE)
+
+        assert cp.returncode == 0
+        assert cp.stdout.split()[0] == b'Python'
+        assert cp.stdout.split()[1].startswith(b'3.5')
+
+    def test_execute_cmderror(self):
+        cmd = 'bzr cat bzr://bzr.sv.gnu.org/gnewsense/packages-parkes/nonexistent-packages/debian/README.gNewSense'
+        cp = execute(cmd, err=subprocess.PIPE)
+
+        assert cp.returncode == 3
+        assert cp.stderr.startswith(b'bzr: ERROR:')
+
+
+    @raises(SystemExit)
+    def test_execute_raise_exception(self):
+        cmd = 'cornhole computers'
+        with open(os.devnull, 'w') as sys.stderr:
+            cp = execute(cmd)
+
+
     def test_get_packages(self):
         pkgs_iter = get_packages(self.pkgs_file)
         assert len(list(pkgs_iter)) == 82