Add tests for .cd dot command

awsshell/app.py

@@ -46,16 +46,21 @@ class InputInterrupt(Exception):
 
 
 class ChangeDirHandler(object):
+    def __init__(self, output=sys.stdout, err=sys.stderr, chdir=os.chdir):
+        self._output = output
+        self._err = err
+        self._chdir = chdir
+
     def run(self, command, application):
         # command is a list of parsed commands
         if len(command) != 2:
-            sys.stderr.write("invalid syntax, must be: .cd dirname\n")
+            self._err.write("invalid syntax, must be: .cd dirname\n")
             return
         dirname = os.path.expandvars(os.path.expanduser(command[1]))
         try:
-            os.chdir(dirname)
+            self._chdir(dirname)
         except OSError as e:
-            sys.stderr.write("cd: %s\n" % e)
+            self._err.write("cd: %s\n" % e)
 
 
 class EditHandler(object):

tests/unit/test_app.py

@@ -42,3 +42,26 @@ def test_prints_error_message_on_unknown_dot_command(errstream):
     handler = app.DotCommandHandler(err=errstream)
     handler.handle_cmd(".unknown foo bar", None)
     assert errstream.getvalue() == "Unknown dot command: .unknown\n"
+
+
+def test_cd_handler_can_chdir():
+    chdir = mock.Mock()
+    handler = app.ChangeDirHandler(chdir=chdir)
+    handler.run(['.cd', 'foo/bar'], None)
+    assert chdir.call_args == mock.call('foo/bar')
+
+
+def test_chdir_syntax_error_prints_err_msg(errstream):
+    chdir = mock.Mock()
+    handler = app.ChangeDirHandler(err=errstream, chdir=chdir)
+    handler.run(['.cd'], None)
+    assert 'invalid syntax' in errstream.getvalue()
+    assert not chdir.called
+
+
+def test_error_displayed_when_chdir_fails(errstream):
+    chdir = mock.Mock()
+    chdir.side_effect = OSError("FAILED")
+    handler = app.ChangeDirHandler(err=errstream, chdir=chdir)
+    handler.run(['.cd', 'foo'], None)
+    assert 'FAILED' in errstream.getvalue()