diff --git a/mimo/connection/connection.py b/mimo/connection/connection.py
index 5cb6479..50148c7 100644
--- a/mimo/connection/connection.py
+++ b/mimo/connection/connection.py
@@ -11,5 +11,8 @@ def __init__(self, name, threshold=10):
     def __len__(self):
         return len(self.entities)
 
+    def clear(self):
+        self.entities.clear()
+
     def is_full(self):
         return len(self.entities) >= self.threshold
diff --git a/mimo/test_helper.py b/mimo/test_helper.py
new file mode 100644
index 0000000..c351958
--- /dev/null
+++ b/mimo/test_helper.py
@@ -0,0 +1,23 @@
+from .connection.input import Input
+from .connection.output import Output
+from .connection.connection_set import ConnectionSet
+
+
+class TestHelper:
+    def __init__(self, stream):
+        ins = [Input(in_) for in_ in stream.ins]
+        outs = [Output(out) for out in stream.outs]
+        self.ins = ConnectionSet(ins)
+        self.outs = ConnectionSet(outs)
+        self.stream = stream
+
+    def run(self, ins):
+        for key, value in ins.items():
+            self.ins[key].clear()
+            self.ins[key].extend(value)
+        outs = {out.name: [] for out in self.outs}
+        while self.stream.run(self.ins, self.outs):
+            for out in self.outs:
+                outs[out.name].extend(out.entities)
+                out.clear()
+        return outs
diff --git a/mimo/workflow/workflow.py b/mimo/workflow/workflow.py
index 8a6deb9..6dd1aad 100644
--- a/mimo/workflow/workflow.py
+++ b/mimo/workflow/workflow.py
@@ -49,7 +49,7 @@ def run(self):
                     continue
                 for input in inputs:
                     input.extend(output.entities)
-                output.entities.clear()
+                output.clear()
                 for input_id in input_ids:
                     stream_ids = self.graph.get_children(input_id)
                     stack.extend(stream_id for stream_id in stream_ids if stream_id not in stacked)
diff --git a/tests/test_stream/test_stream.py b/tests/test_stream/test_stream.py
index 263782a..3e3aceb 100644
--- a/tests/test_stream/test_stream.py
+++ b/tests/test_stream/test_stream.py
@@ -15,12 +15,12 @@ def test_run(self):
         outs = ConnectionSet([output])
         input.entities.extend([1, 2, 3, 4, 5, 6, 7, 8, 9, 0])
 
-        stream.run(ins, outs)
+        self.assertTrue(stream.run(ins, outs))
         self.assertEqual([2, 4, 6, 8, 10], list(output.entities))
-        stream.run(ins, outs)
+        self.assertTrue(stream.run(ins, outs))
         self.assertEqual([2, 4, 6, 8, 10, 12], list(output.entities))
         output.entities.clear()
-        stream.run(ins, outs)
+        self.assertFalse(stream.run(ins, outs))
         self.assertEqual([14, 16, 18, 0], list(output.entities))
 
 
diff --git a/tests/test_test_helper.py b/tests/test_test_helper.py
new file mode 100644
index 0000000..338b384
--- /dev/null
+++ b/tests/test_test_helper.py
@@ -0,0 +1,23 @@
+import unittest
+
+from mimo import Stream
+from mimo.test_helper import TestHelper
+
+
+class TestTestHelper(unittest.TestCase):
+    def test_run(self):
+        stream = Stream(ins=['a'], outs=['b'], fn=fn)
+        helper = TestHelper(stream)
+
+        self.assertEqual({'b': [2, 4, 6, 8, 10, 12, 14, 16, 18, 0]},
+                         helper.run({'a': [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]}))
+
+
+def fn(ins, outs, state):
+    while len(ins.a) > 0:
+        if not outs.b.push(2 * ins.a.pop()):
+            return True
+
+
+if __name__ == '__main__':
+    unittest.main()