Test for parallel_execute with limit

Signed-off-by: Evan Shaw <evan@vendhq.com>

tests/unit/parallel_test.py

@@ -1,6 +1,8 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 
+from threading import Lock
+
 import six
 from docker.errors import APIError
 
@@ -40,6 +42,30 @@ def test_parallel_execute():
     assert errors == {}
 
 
+def test_parallel_execute_with_limit():
+    limit = 1
+    tasks = 20
+    lock = Lock()
+
+    def f(obj):
+        locked = lock.acquire(False)
+        # we should always get the lock because we're the only thread running
+        assert locked
+        lock.release()
+        return None
+
+    results, errors = parallel_execute(
+        objects=list(range(tasks)),
+        func=f,
+        get_name=six.text_type,
+        msg="Testing",
+        limit=limit,
+    )
+
+    assert results == tasks*[None]
+    assert errors == {}
+
+
 def test_parallel_execute_with_deps():
     log = []