Add unit test for execute_cmd in repo2docker.utils

repo2docker/utils.py

@@ -10,7 +10,9 @@ from traitlets import Integer, TraitError
 
 def execute_cmd(cmd, capture=False, **kwargs):
     """
-    Call given command, yielding output line by line if capture=True
+    Call given command, yielding output line by line if capture=True.
+
+    Must be yielded from.
     """
     if capture:
         kwargs['stdout'] = subprocess.PIPE

tests/test_utils.py

@@ -0,0 +1,37 @@
+"""
+Tests for repo2docker/utils.py
+"""
+from repo2docker import utils
+import pytest
+import subprocess
+
+
+def test_capture_cmd_no_capture_success():
+    # This should succeed
+    for line in utils.execute_cmd([
+        '/bin/bash', '-c', 'echo test'
+    ]):
+        pass
+
+def test_capture_cmd_no_capture_fail():
+    with pytest.raises(subprocess.CalledProcessError):
+        for line in utils.execute_cmd([
+            '/bin/bash', '-c', 'e '
+        ]):
+            pass
+
+
+def test_capture_cmd_capture_success():
+    # This should succeed
+    for line in utils.execute_cmd([
+        '/bin/bash', '-c', 'echo test'
+    ], capture=True):
+        assert line == 'test\n'
+
+
+def test_capture_cmd_capture_fail():
+    with pytest.raises(subprocess.CalledProcessError):
+        for line in utils.execute_cmd([
+            '/bin/bash', '-c', 'echo test; exit 1 '
+        ], capture=True):
+            assert line == 'test\n'