diff --git a/GPy/testing/cython_tests.py b/GPy/testing/cython_tests.py
index dc41c44a..1ad23121 100644
--- a/GPy/testing/cython_tests.py
+++ b/GPy/testing/cython_tests.py
@@ -8,13 +8,15 @@ from ..util.config import config
 
 try:
     from ..util import choleskies_cython
-    choleskies_cython_working = config.getboolean('cython', 'working')
+
+    choleskies_cython_working = config.getboolean("cython", "working")
 except ImportError:
     choleskies_cython_working = False
 
 try:
     from ..kern.src import stationary_cython
-    stationary_cython_working = config.getboolean('cython', 'working')
+
+    stationary_cython_working = config.getboolean("cython", "working")
 except ImportError:
     stationary_cython_working = False
 
@@ -22,29 +24,39 @@ except ImportError:
 These tests make sure that the pure python and cython codes work the same
 """
 
-@unittest.skipIf(not choleskies_cython_working,"Cython cholesky module has not been built on this machine")
+
+@unittest.skipIf(
+    not choleskies_cython_working,
+    "Cython cholesky module has not been built on this machine",
+)
 class CythonTestChols(np.testing.TestCase):
     def setUp(self):
-        self.flat = np.random.randn(45,5)
+        self.flat = np.random.randn(45, 5)
         self.triang = np.array([np.eye(20) for i in range(3)])
+
     def test_flat_to_triang(self):
         L1 = choleskies._flat_to_triang_pure(self.flat)
         L2 = choleskies._flat_to_triang_cython(self.flat)
         np.testing.assert_allclose(L1, L2)
+
     def test_triang_to_flat(self):
         A1 = choleskies._triang_to_flat_pure(self.triang)
         A2 = choleskies._triang_to_flat_cython(self.triang)
         np.testing.assert_allclose(A1, A2)
 
-@unittest.skipIf(not stationary_cython_working,"Cython stationary module has not been built on this machine")
+
+@unittest.skipIf(
+    not stationary_cython_working,
+    "Cython stationary module has not been built on this machine",
+)
 class test_stationary(np.testing.TestCase):
     def setUp(self):
         self.k = GPy.kern.RBF(10)
-        self.X = np.random.randn(300,10)
-        self.Z = np.random.randn(20,10)
-        self.dKxx = np.random.randn(300,300)
-        self.dKzz = np.random.randn(20,20)
-        self.dKxz = np.random.randn(300,20)
+        self.X = np.random.randn(300, 10)
+        self.Z = np.random.randn(20, 10)
+        self.dKxx = np.random.randn(300, 300)
+        self.dKzz = np.random.randn(20, 20)
+        self.dKxz = np.random.randn(300, 20)
 
     def test_square_gradX(self):
         g1 = self.k._gradients_X_cython(self.dKxx, self.X)
@@ -66,13 +78,18 @@ class test_stationary(np.testing.TestCase):
         g2 = self.k._lengthscale_grads_cython(self.dKxz, self.X, self.Z)
         np.testing.assert_allclose(g1, g2)
 
-@unittest.skipIf(not choleskies_cython_working,"Cython cholesky module has not been built on this machine")
+
+@unittest.skipIf(
+    not choleskies_cython_working,
+    "Cython cholesky module has not been built on this machine",
+)
 class test_choleskies_backprop(np.testing.TestCase):
     def setUp(self):
-        a =np.random.randn(10,12)
+        a = np.random.randn(10, 12)
         A = a.dot(a.T)
         self.L = GPy.util.linalg.jitchol(A)
-        self.dL = np.random.randn(10,10)
+        self.dL = np.random.randn(10, 10)
+
     def test(self):
         r1 = choleskies._backprop_gradient_pure(self.dL, self.L)
         r2 = choleskies_cython.backprop_gradient(self.dL, self.L)