diff --git a/tests/test_krige.py b/tests/test_krige.py
index 6d4d935d..af7984b4 100644
--- a/tests/test_krige.py
+++ b/tests/test_krige.py
@@ -5,16 +5,20 @@
 
 import numpy as np
 import unittest
-from gstools import Gaussian, Exponential, Spherical, krige, SRF
+import gstools as gs
 
 
 def trend(*xyz):
     return xyz[0]
 
 
+def mean_func(*xyz):
+    return 2 * xyz[0]
+
+
 class TestKrige(unittest.TestCase):
     def setUp(self):
-        self.cov_models = [Gaussian, Exponential, Spherical]
+        self.cov_models = [gs.Gaussian, gs.Exponential, gs.Spherical]
         self.dims = range(1, 4)
         self.data = np.array(
             [
@@ -58,7 +62,7 @@ def test_simple(self):
                     anis=[0.9, 0.8],
                     angles=[2, 1, 0.5],
                 )
-                simple = krige.Simple(
+                simple = gs.krige.Simple(
                     model, self.cond_pos[:dim], self.cond_val, self.mean
                 )
                 field_1, __ = simple.unstructured(self.grids[dim - 1])
@@ -83,7 +87,7 @@ def test_ordinary(self):
                         anis=[0.9, 0.8],
                         angles=[2, 1, 0.5],
                     )
-                    ordinary = krige.Ordinary(
+                    ordinary = gs.krige.Ordinary(
                         model,
                         self.cond_pos[:dim],
                         self.cond_val,
@@ -112,7 +116,7 @@ def test_universal(self):
                         anis=[0.9, 0.8],
                         angles=[2, 1, 0.5],
                     )
-                    universal = krige.Universal(
+                    universal = gs.krige.Universal(
                         model, self.cond_pos[:dim], self.cond_val, drift
                     )
                     field_1, __ = universal.unstructured(self.grids[dim - 1])
@@ -137,7 +141,7 @@ def test_detrended(self):
                     anis=[0.5, 0.2],
                     angles=[0.4, 0.2, 0.1],
                 )
-                detrended = krige.Detrended(
+                detrended = gs.krige.Detrended(
                     model, self.cond_pos[:dim], self.cond_val, trend
                 )
                 field_1, __ = detrended.unstructured(self.grids[dim - 1])
@@ -157,14 +161,14 @@ def test_extdrift(self):
         cond_drift = []
         for i, grid in enumerate(self.grids):
             dim = i + 1
-            model = Exponential(
+            model = gs.Exponential(
                 dim=dim,
                 var=2,
                 len_scale=10,
                 anis=[0.9, 0.8],
                 angles=[2, 1, 0.5],
             )
-            srf = SRF(model)
+            srf = gs.SRF(model)
             field = srf(grid)
             ext_drift.append(field)
             field = field.reshape(self.grid_shape[:dim])
@@ -179,7 +183,7 @@ def test_extdrift(self):
                     anis=[0.5, 0.2],
                     angles=[0.4, 0.2, 0.1],
                 )
-                extdrift = krige.ExtDrift(
+                extdrift = gs.krige.ExtDrift(
                     model,
                     self.cond_pos[:dim],
                     self.cond_val,
@@ -202,7 +206,6 @@ def test_extdrift(self):
                     )
 
     def test_pseudo(self):
-
         for Model in self.cov_models:
             for dim in self.dims:
                 model = Model(
@@ -213,7 +216,7 @@ def test_pseudo(self):
                     angles=[0.4, 0.2, 0.1],
                 )
                 for meth in self.p_meth:
-                    krig = krige.Krige(
+                    krig = gs.krige.Krige(
                         model, self.p_data[:dim], self.p_vals, unbiased=False
                     )
                     field, __ = krig([0, 0, 0][:dim])
@@ -224,7 +227,6 @@ def test_pseudo(self):
                     )
 
     def test_error(self):
-
         for Model in self.cov_models:
             for dim in self.dims:
                 model = Model(
@@ -235,7 +237,7 @@ def test_error(self):
                     anis=[0.9, 0.8],
                     angles=[2, 1, 0.5],
                 )
-                ordinary = krige.Ordinary(
+                ordinary = gs.krige.Ordinary(
                     model,
                     self.cond_pos[:dim],
                     self.cond_val,
@@ -248,6 +250,42 @@ def test_error(self):
                 self.assertAlmostEqual(err[1], model.nugget, places=2)
                 self.assertAlmostEqual(err[4], model.nugget, places=2)
 
+    def test_raise(self):
+        # no cond_pos/cond_val given
+        self.assertRaises(ValueError, gs.krige.Krige, gs.Stable(), None, None)
+
+    def test_krige_mean(self):
+        # check for constant mean (simple kriging)
+        krige = gs.krige.Simple(gs.Gaussian(), self.cond_pos, self.cond_val)
+        mean_f = krige.structured(self.pos, only_mean=True)
+        self.assertTrue(np.all(np.isclose(mean_f, 0)))
+        krige = gs.krige.Simple(
+            gs.Gaussian(),
+            self.cond_pos,
+            self.cond_val,
+            mean=mean_func,
+            normalizer=gs.normalizer.YeoJohnson,
+            trend=trend,
+        )
+        # check applying mean, norm, trend
+        mean_f1 = krige.structured(self.pos, only_mean=True)
+        mean_f2 = gs.normalizer.tools.apply_mean_norm_trend(
+            self.pos,
+            np.zeros(tuple(map(len, self.pos))),
+            mean=mean_func,
+            normalizer=gs.normalizer.YeoJohnson,
+            trend=trend,
+            mesh_type="structured",
+        )
+        self.assertTrue(np.all(np.isclose(mean_f1, mean_f2)))
+        krige = gs.krige.Simple(gs.Gaussian(), self.cond_pos, self.cond_val)
+        mean_f = krige.structured(self.pos, only_mean=True)
+        self.assertTrue(np.all(np.isclose(mean_f, 0)))
+        # check for constant mean (ordinary kriging)
+        krige = gs.krige.Ordinary(gs.Gaussian(), self.cond_pos, self.cond_val)
+        mean_f = krige.structured(self.pos, only_mean=True)
+        self.assertTrue(np.all(np.isclose(mean_f, krige.get_mean())))
+
 
 if __name__ == "__main__":
     unittest.main()