diff --git a/conftest.py b/conftest.py
index c20bde40916e7f7f5163c20e1c48c7b0f3d3b3a2..78164d005760abacfac7f13ab7fab365f8f31c19 100644
--- a/conftest.py
+++ b/conftest.py
@@ -44,7 +44,7 @@ collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils/autodiff.py")]
 try:
     import pycuda
 except ImportError:
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils/pystencils_tests/test_cudagpu.py")]
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils_tests/test_cudagpu.py")]
     add_path_to_ignore('pystencils/gpucuda')
 
 try:
@@ -73,7 +73,22 @@ try:
     import blitzdb
 except ImportError:
     add_path_to_ignore('pystencils/runhelper')
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils_tests/test_parameterstudy.py")]
 
+try:
+    import islpy
+except ImportError:
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils/integer_set_analysis.py")]
+
+try:
+    import graphviz
+except ImportError:
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils/backends/dot.py")]
+
+try:
+    import pyevtk
+except ImportError:
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "pystencils/datahandling/vtk.py")]
 
 collect_ignore += [os.path.join(SCRIPT_FOLDER, 'setup.py')]
 
@@ -131,7 +146,7 @@ class IPyNbFile(pytest.File):
         exporter.exclude_markdown = True
         exporter.exclude_input_prompt = True
 
-        notebook_contents = self.fspath.open()
+        notebook_contents = self.fspath.open(encoding='utf-8')
 
         with warnings.catch_warnings():
             warnings.filterwarnings("ignore", "IPython.core.inputsplitter is deprecated")
diff --git a/pystencils/kernelcreation.py b/pystencils/kernelcreation.py
index aaca6d3124c4303ae289e831fdb7b7680369c408..2c8aabaa530f985f7b645a41a29a9537a655fa07 100644
--- a/pystencils/kernelcreation.py
+++ b/pystencils/kernelcreation.py
@@ -79,14 +79,14 @@ def create_kernel(assignments,
                [0., 0., 0., 0., 0.]])
     """
     # ----  Normalizing parameters
+    if isinstance(assignments, Assignment):
+        assignments = [assignments]
     assert assignments, "Assignments must not be empty!"
     split_groups = ()
     if isinstance(assignments, AssignmentCollection):
         if 'split_groups' in assignments.simplification_hints:
             split_groups = assignments.simplification_hints['split_groups']
         assignments = assignments.all_assignments
-    if isinstance(assignments, Assignment):
-        assignments = [assignments]
 
     # ----  Creating ast
     if target == 'cpu':
diff --git a/pystencils_tests/test_custom_backends.py b/pystencils_tests/test_custom_backends.py
index 1ff775d41355b79c1714a935125f27c261045011..692f78894e253cb22292555389d9f9c21a5e5ade 100644
--- a/pystencils_tests/test_custom_backends.py
+++ b/pystencils_tests/test_custom_backends.py
@@ -1,6 +1,5 @@
 from subprocess import CalledProcessError
 
-import pycuda.driver
 import pytest
 import sympy
 
@@ -25,7 +24,7 @@ class ScreamingGpuBackend(CudaBackend):
         return normal_code.upper()
 
 
-def test_custom_backends():
+def test_custom_backends_cpu():
     z, x, y = pystencils.fields("z, y, x: [2d]")
 
     normal_assignments = pystencils.AssignmentCollection([pystencils.Assignment(
@@ -36,6 +35,16 @@ def test_custom_backends():
     with pytest.raises(CalledProcessError):
         pystencils.cpu.cpujit.make_python_function(ast, custom_backend=ScreamingBackend())
 
+
+def test_custom_backends_gpu():
+    pytest.importorskip('pycuda')
+    import pycuda.driver
+
+    z, x, y = pystencils.fields("z, y, x: [2d]")
+
+    normal_assignments = pystencils.AssignmentCollection([pystencils.Assignment(
+        z[0, 0], x[0, 0] * sympy.log(x[0, 0] * y[0, 0]))], [])
+
     ast = pystencils.create_kernel(normal_assignments, target='gpu')
     print(pystencils.show_code(ast, ScreamingGpuBackend()))
     with pytest.raises(pycuda.driver.CompileError):
diff --git a/pystencils_tests/test_interpolation.py b/pystencils_tests/test_interpolation.py
index dd4ee06f4ba9197111a04af572df6cdaf2695ab5..0776a7de02347bbb518c37d6d7999b7ad0aff9a0 100644
--- a/pystencils_tests/test_interpolation.py
+++ b/pystencils_tests/test_interpolation.py
@@ -11,8 +11,6 @@ import itertools
 from os.path import dirname, join
 
 import numpy as np
-import pycuda.autoinit  # NOQA
-import pycuda.gpuarray as gpuarray
 import pytest
 import sympy
 
@@ -112,6 +110,9 @@ def test_rotate_interpolation(address_mode):
 
 @pytest.mark.parametrize('address_mode', ['border', 'wrap', 'clamp', 'mirror'])
 def test_rotate_interpolation_gpu(address_mode):
+    pytest.importorskip('pycuda')
+    import pycuda.autoinit  # NOQA
+    import pycuda.gpuarray as gpuarray
 
     rotation_angle = sympy.pi / 5
     scale = 1
@@ -156,6 +157,9 @@ def test_rotate_interpolation_gpu(address_mode):
 
 @pytest.mark.parametrize('address_mode', ['border', 'wrap', 'clamp', 'mirror'])
 def test_shift_interpolation_gpu(address_mode):
+    pytest.importorskip('pycuda')
+    import pycuda.autoinit  # NOQA
+    import pycuda.gpuarray as gpuarray
 
     rotation_angle = 0  # sympy.pi / 5
     scale = 1