[unit] Improve PinocchioTestCase

unittest/python/test_case.py

@@ -9,5 +9,6 @@ def tracefunc(frame, event, arg):
     return tracefunc
 
 class PinocchioTestCase(unittest.TestCase):
-    def assertApprox(self, a, b):
-        return self.assertTrue(isapprox(a, b))
+    def assertApprox(self, a, b, eps=1e-6):
+        return self.assertTrue(isapprox(a, b, eps),
+                               "\n%s\nis not approximately equal to\n%s\nwith precision %f" % (a, b, eps))