DEV: Add parameter_space test decorator.

tests/test_test_utils.py

@@ -0,0 +1,31 @@
+"""
+Tests for our testing utilities.
+"""
+from itertools import product
+from unittest import TestCase
+from zipline.utils.test_utils import parameter_space
+
+
+class TestParameterSpace(TestCase):
+
+    x_args = [1, 2]
+    y_args = [3, 4]
+
+    @classmethod
+    def setUpClass(cls):
+        cls.xy_invocations = []
+
+    @classmethod
+    def tearDownClass(cls):
+        # This is the only actual test here.
+        assert cls.xy_invocations == list(product(cls.x_args, cls.y_args))
+
+    @parameter_space(x=x_args, y=y_args)
+    def test_xy(self, x, y):
+        self.xy_invocations.append((x, y))
+
+    def test_nothing(self):
+        # Ensure that there's at least one "real" test in the class, or else
+        # our {setUp,tearDown}Class won't be called if, for example,
+        # `parameter_space` returns None.
+        pass