Test semilagrangian extrapolation with list of timesteps (#319)

pysteps/tests/test_extrapolation_semilagrangian.py

@@ -6,16 +6,36 @@
 
 
 def test_semilagrangian():
-    """Tests semilagrangian extrapolation."""
+    """Test semilagrangian extrapolation with number of timesteps."""
     # inputs
-    precip = np.ones((8, 8))
+    precip = np.zeros((8, 8))
+    precip[0, 0] = 1
     v = np.ones((8, 8))
     velocity = np.stack([v, v])
     num_timesteps = 1
     # expected
-    expected = np.ones((1, 8, 8))
+    expected = np.zeros((1, 8, 8))
     expected[:, :, 0] = np.nan
     expected[:, 0, :] = np.nan
+    expected[:, 1, 1] = 1
     # result
     result = extrapolate(precip, velocity, num_timesteps)
     assert_array_almost_equal(result, expected)
+
+
+def test_semilagrangian_timesteps():
+    """Test semilagrangian extrapolation with list of timesteps."""
+    # inputs
+    precip = np.zeros((8, 8))
+    precip[0, 0] = 1
+    v = np.ones((8, 8)) * 10
+    velocity = np.stack([v, v])
+    timesteps = [0.1]
+    # expected
+    expected = np.zeros((1, 8, 8))
+    expected[:, :, 0] = np.nan
+    expected[:, 0, :] = np.nan
+    expected[:, 1, 1] = 1
+    # result
+    result = extrapolate(precip, velocity, timesteps)
+    assert_array_almost_equal(result, expected)