diff --git a/plugins/catalog/src/components/SystemDiagram/SystemDiagram.test.tsx b/plugins/catalog/src/components/SystemDiagram/SystemDiagram.test.tsx
new file mode 100644
index 0000000000..648df0cff3
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+++ b/plugins/catalog/src/components/SystemDiagram/SystemDiagram.test.tsx
@@ -0,0 +1,99 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { catalogApiRef } from '@backstage/catalog-client';
+import { Entity, RELATION_HAS_PART } from '@backstage/catalog-model';
+import { CatalogApi, EntityProvider } from '@backstage/plugin-catalog-react';
+import { renderInTestApp } from '@backstage/test-utils';
+import { waitFor } from '@testing-library/react';
+import React from 'react';
+import { SystemDiagram } from './SystemDiagram';
+
+describe('<SystemDiagram />', () => {
+  const catalogApi: jest.Mocked<CatalogApi> = {
+    getLocationById: jest.fn(),
+    getEntityByName: jest.fn(),
+    getEntities: jest.fn(),
+    addLocation: jest.fn(),
+    getLocationByEntity: jest.fn(),
+    removeEntityByUid: jest.fn(),
+  } as any;
+
+  afterEach(() => jest.resetAllMocks());
+
+  it('shows empty list if no relations', async () => {
+    const entity: Entity = {
+      apiVersion: 'v1',
+      kind: 'Domain',
+      metadata: {
+        name: 'my-domain',
+        namespace: 'my-namespace',
+      },
+      relations: [],
+    };
+
+    const { getByText } = await renderInTestApp(
+      <EntityProvider entity={entity}>
+        <SystemDiagram entity={entity} />
+      </EntityProvider>,
+    );
+
+    expect(getByText('System Diagram')).toBeInTheDocument();
+    // expect(getByText('Systems')).toBeInTheDocument();
+    // expect(getByText(/No system is part of this domain/i)).toBeInTheDocument();
+  });
+
+  it('shows related systems', async () => {
+    const entity: Entity = {
+      apiVersion: 'v1',
+      kind: 'Domain',
+      metadata: {
+        name: 'my-domain',
+        namespace: 'my-namespace',
+      },
+      relations: [
+        {
+          target: {
+            kind: 'System',
+            namespace: 'my-namespace',
+            name: 'target-name',
+          },
+          type: RELATION_HAS_PART,
+        },
+      ],
+    };
+    catalogApi.getEntityByName.mockResolvedValue({
+      apiVersion: 'v1',
+      kind: 'System',
+      metadata: {
+        name: 'target-name',
+        namespace: 'my-namespace',
+      },
+      spec: {},
+    });
+
+    const { getByText } = await renderInTestApp(
+      <EntityProvider entity={entity}>
+        <SystemDiagram entity={entity} />
+      </EntityProvider>,
+    );
+
+    await waitFor(() => {
+      expect(getByText('Systems')).toBeInTheDocument();
+      expect(getByText(/target-name/i)).toBeInTheDocument();
+    });
+  });
+});