diff --git a/light9/effecteval/test_effect.py b/light9/effecteval/test_effect.py
--- a/light9/effecteval/test_effect.py
+++ b/light9/effecteval/test_effect.py
@@ -10,43 +10,56 @@ def isCurve(self, uri):
     return 'curve' in uri
 
 @mock.patch('light9.effecteval.effect.CodeLine._uriIsCurve', new=isCurve)
+@mock.patch('light9.effecteval.effect.CodeLine._resourcesAsPython',
+            new=lambda self, r: self.expr)
 class TestAsPython(unittest.TestCase):
     def test_gets_lname(self):
         ec = CodeLine(graph=None, code='x = y+1')
-        self.assertEqual('x', ec._asPython()[0])
+        self.assertEqual('x', ec.outName)
 
     def test_gets_simple_code(self):
         ec = CodeLine(graph=None, code='x = y+1')
-        self.assertEqual('y+1', ec._asPython()[1])
-        self.assertEqual({}, ec._asPython()[2])
+        self.assertEqual('y+1', ec._asPython()[2])
+        self.assertEqual({}, ec._asPython()[3])
         
     def test_converts_uri_to_var(self):
         ec = CodeLine(graph=None, code='x = <http://example.com/>')
-        _, expr, uris = ec._asPython()
+        _, inExpr, expr, uris = ec._asPython()
         self.assertEqual('_res0', expr)
         self.assertEqual({'_res0': URIRef('http://example.com/')}, uris)
 
     def test_converts_multiple_uris(self):
         ec = CodeLine(graph=None, code='x = <http://example.com/> + <http://other>')
-        _, expr, uris = ec._asPython()
+        _, inExpr, expr, uris = ec._asPython()
         self.assertEqual('_res0 + _res1', expr)
         self.assertEqual({'_res0': URIRef('http://example.com/'),
                           '_res1': URIRef('http://other')}, uris)
         
     def test_doesnt_fall_for_brackets(self):
         ec = CodeLine(graph=None, code='x = 1<2>3< h')
-        _, expr, uris = ec._asPython()
+        _, inExpr, expr, uris = ec._asPython()
         self.assertEqual('1<2>3< h', expr)
         self.assertEqual({}, uris)
         
     def test_curve_uri_expands_to_curve_eval_func(self):
         ec = CodeLine(graph=None, code='x = <http://example/curve1>')
-        _, expr, uris = ec._asPython()
+        _, inExpr, expr, uris = ec._asPython()
         self.assertEqual('curve(_res0, t)', expr)
         self.assertEqual({'_res0': URIRef('http://example/curve1')}, uris)
 
     def test_curve_doesnt_double_wrap(self):
         ec = CodeLine(graph=None, code='x = curve(<http://example/curve1>, t+.01)')
-        _, expr, uris = ec._asPython()
+        _, inExpr, expr, uris = ec._asPython()
         self.assertEqual('curve(_res0, t+.01)', expr)
         self.assertEqual({'_res0': URIRef('http://example/curve1')}, uris)
+
+@mock.patch('light9.effecteval.effect.CodeLine._uriIsCurve', new=isCurve)
+@mock.patch('light9.effecteval.effect.CodeLine._resourcesAsPython',
+            new=lambda self, r: self.expr)
+class TestPossibleVars(unittest.TestCase):
+    def test1(self):
+        self.assertEqual(set([]), CodeLine(None, 'a1 = 1').possibleVars)
+    def test2(self):
+        self.assertEqual(set(['a2']), CodeLine(None, 'a1 = a2').possibleVars)
+    def test3(self):
+        self.assertEqual(set(['a2', 'a3']), CodeLine(None, 'a1 = a2 + a3').possibleVars)