diff --git a/tests/test_energy_system.py b/tests/test_energy_system.py
new file mode 100644
index 0000000..6a789f8
--- /dev/null
+++ b/tests/test_energy_system.py
@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -
+
+"""Basic tests.
+
+This file is part of project oemof.network (github.com/oemof/oemof-network).
+
+SPDX-FileCopyrightText: Stephan Günther <>
+SPDX-FileCopyrightText: Uwe Krien <krien@uni-bremen.de>
+SPDX-FileCopyrightText: Simon Hilpert <>
+SPDX-FileCopyrightText: Cord Kaldemeyer <>
+SPDX-FileCopyrightText: Patrik Schönfeldt <patrik.schoenfeldt@dlr.de>
+
+SPDX-License-Identifier: MIT
+"""
+from itertools import chain
+
+from oemof.network import energy_system as es
+from oemof.network.groupings import Flows
+from oemof.network.groupings import FlowsWithNodes as FWNs
+from oemof.network.network import Bus
+from oemof.network.network.nodes import Node
+
+
+class TestsEnergySystem:
+    def setup_method(self):
+        self.es = es.EnergySystem()
+
+    def test_flows(self):
+        key = object()
+        ensys = es.EnergySystem(groupings=[Flows(key)])
+        bus = Bus(label="A Bus")
+        node = Node(label="A Node", inputs={bus: None}, outputs={bus: None})
+        ensys.add(bus, node)
+        assert ensys.groups[key] == set(
+            chain(bus.inputs.values(), bus.outputs.values())
+        )
+
+    def test_flows_with_nodes(self):
+        key = object()
+        ensys = es.EnergySystem(groupings=[FWNs(key)])
+        bus = Bus(label="A Bus")
+        node = Node(label="A Node", inputs={bus: None}, outputs={bus: None})
+        ensys.add(bus, node)
+        assert ensys.groups[key], {
+            (bus, node, bus.outputs[node]),
+            (node, bus, node.outputs[bus]),
+        }
+
+    def test_that_node_additions_are_signalled(self):
+        """
+        When a node gets `add`ed, a corresponding signal should be emitted.
+        """
+        node = Node(label="Node")
+
+        def subscriber(sender, **kwargs):
+            assert sender is node
+            assert kwargs["EnergySystem"] is self.es
+            subscriber.called = True
+
+        subscriber.called = False
+
+        es.EnergySystem.signals[es.EnergySystem.add].connect(
+            subscriber, sender=node
+        )
+        self.es.add(node)
+        assert subscriber.called, (
+            "\nExpected `subscriber.called` to be `True`.\n"
+            "Got {}.\n"
+            "Probable reason: `subscriber` didn't get called."
+        ).format(subscriber.called)
diff --git a/tests/test_groupings.py b/tests/test_groupings/test_groupings_advanced.py
similarity index 100%
rename from tests/test_groupings.py
rename to tests/test_groupings/test_groupings_advanced.py
diff --git a/tests/basic_tests.py b/tests/test_groupings/test_groupings_basic.py
similarity index 78%
rename from tests/basic_tests.py
rename to tests/test_groupings/test_groupings_basic.py
index 94f111b..7d3a8a0 100644
--- a/tests/basic_tests.py
+++ b/tests/test_groupings/test_groupings_basic.py
@@ -2,9 +2,7 @@
 
 """Basic tests.
 
-This file is part of project oemof (github.com/oemof/oemof). It's copyrighted
-by the contributors recorded in the version control history of the file,
-available from its original location oemof/tests/basic_tests.py
+This file is part of project oemof.network (github.com/oemof/oemof-network).
 
 SPDX-FileCopyrightText: Stephan Günther <>
 SPDX-FileCopyrightText: Uwe Krien <krien@uni-bremen.de>
@@ -15,13 +13,10 @@
 SPDX-License-Identifier: MIT
 """
 from collections.abc import Iterable
-from itertools import chain
 from pprint import pformat
 
 from oemof.network import energy_system as es
 from oemof.network.groupings import Entities
-from oemof.network.groupings import Flows
-from oemof.network.groupings import FlowsWithNodes as FWNs
 from oemof.network.groupings import Grouping
 from oemof.network.network import Bus
 from oemof.network.network.nodes import Node
@@ -188,47 +183,3 @@ def everything():
         assert everything in ensys.groups
         assert ensys.groups[everything] == {node}
         assert everything() == "everything"
-
-    def test_flows(self):
-        key = object()
-        ensys = es.EnergySystem(groupings=[Flows(key)])
-        bus = Bus(label="A Bus")
-        node = Node(label="A Node", inputs={bus: None}, outputs={bus: None})
-        ensys.add(bus, node)
-        assert ensys.groups[key] == set(
-            chain(bus.inputs.values(), bus.outputs.values())
-        )
-
-    def test_flows_with_nodes(self):
-        key = object()
-        ensys = es.EnergySystem(groupings=[FWNs(key)])
-        bus = Bus(label="A Bus")
-        node = Node(label="A Node", inputs={bus: None}, outputs={bus: None})
-        ensys.add(bus, node)
-        assert ensys.groups[key], {
-            (bus, node, bus.outputs[node]),
-            (node, bus, node.outputs[bus]),
-        }
-
-    def test_that_node_additions_are_signalled(self):
-        """
-        When a node gets `add`ed, a corresponding signal should be emitted.
-        """
-        node = Node(label="Node")
-
-        def subscriber(sender, **kwargs):
-            assert sender is node
-            assert kwargs["EnergySystem"] is self.es
-            subscriber.called = True
-
-        subscriber.called = False
-
-        es.EnergySystem.signals[es.EnergySystem.add].connect(
-            subscriber, sender=node
-        )
-        self.es.add(node)
-        assert subscriber.called, (
-            "\nExpected `subscriber.called` to be `True`.\n"
-            "Got {}.\n"
-            "Probable reason: `subscriber` didn't get called."
-        ).format(subscriber.called)