diff --git a/packages/backend-common/src/database/SingleConnection.test.ts b/packages/backend-common/src/database/SingleConnection.test.ts
new file mode 100644
index 0000000000..9da256a2c3
--- /dev/null
+++ b/packages/backend-common/src/database/SingleConnection.test.ts
@@ -0,0 +1,116 @@
+/*
+ * 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 { ConfigReader } from '@backstage/config';
+import { createDatabaseClient } from './connection';
+import { SingleConnectionDatabaseManager } from './SingleConnection';
+
+jest.mock('./connection');
+
+describe('SingleConnectionDatabaseManager', () => {
+  const createConfig = (data: any) =>
+    ConfigReader.fromConfigs([
+      {
+        context: '',
+        data,
+      },
+    ]);
+
+  const defaultConfigOptions = {
+    backend: {
+      database: {
+        client: 'pg',
+        connection: {
+          host: 'localhost',
+          user: 'foo',
+          password: 'bar',
+          database: 'foodb',
+        },
+      },
+    },
+  };
+  const defaultConfig = () => createConfig(defaultConfigOptions);
+
+  // This is similar to the ts-jest `mocked` helper.
+  const mocked = (f: Function) => f as jest.Mock;
+
+  describe('SingleConnectionDatabaseManager.fromConfig', () => {
+    it('accesses the backend.database key', () => {
+      const getConfig = jest.fn();
+      const config = defaultConfig();
+      config.getConfig = getConfig;
+
+      SingleConnectionDatabaseManager.fromConfig(config);
+
+      expect(getConfig.mock.calls[0][0]).toEqual('backend.database');
+    });
+  });
+
+  describe('SingleConnectionDatabaseManager.forPlugin', () => {
+    const manager = SingleConnectionDatabaseManager.fromConfig(defaultConfig());
+
+    it('connects to a database scoped to the plugin', async () => {
+      const pluginId = 'test1';
+      await manager.forPlugin(pluginId).getClient();
+
+      expect(mocked(createDatabaseClient).mock.calls).toHaveLength(1);
+      const mockCalls = mocked(createDatabaseClient).mock.calls.splice(-1);
+
+      const callArgs = mockCalls[0];
+      expect(callArgs[0].get()).toEqual(defaultConfigOptions.backend.database);
+      expect(callArgs[1].connection.database).toEqual(
+        `backstage_plugin_${pluginId}`,
+      );
+    });
+
+    it('allows plugins to get alternative databases', async () => {
+      const pluginId = 'test1';
+      const pluginManager = manager.forPlugin(pluginId);
+      await pluginManager.getClient();
+
+      const secondaryDatabase = 'extra';
+      await pluginManager.getClient(secondaryDatabase);
+
+      expect(mocked(createDatabaseClient).mock.calls).toHaveLength(2);
+      const mockCalls = mocked(createDatabaseClient).mock.calls.splice(-2);
+
+      const mainCallArgs = mockCalls[0];
+      const secondaryCallArgs = mockCalls[1];
+      expect(secondaryCallArgs[1].connection.database).toEqual(
+        `backstage_plugin_${pluginId}_${secondaryDatabase}`,
+      );
+      expect(mainCallArgs[1].connection.database).not.toEqual(
+        secondaryCallArgs[1].connection.database,
+      );
+    });
+
+    it('provides different plugins different databases', async () => {
+      const plugin1Id = 'test1';
+      const plugin2Id = 'test2';
+      await manager.forPlugin(plugin1Id).getClient();
+      await manager.forPlugin(plugin2Id).getClient();
+
+      expect(mocked(createDatabaseClient).mock.calls).toHaveLength(2);
+      const mockCalls = mocked(createDatabaseClient).mock.calls.splice(-2);
+
+      const plugin1CallArgs = mockCalls[0];
+      const plugin2CallArgs = mockCalls[1];
+      expect(plugin1CallArgs[1].connection.database).not.toEqual(
+        plugin2CallArgs[1].connection.database,
+      );
+    });
+  });
+});
diff --git a/packages/backend-common/src/database/config.test.ts b/packages/backend-common/src/database/config.test.ts
index ab29bc19ba..c9a4107686 100644
--- a/packages/backend-common/src/database/config.test.ts
+++ b/packages/backend-common/src/database/config.test.ts
@@ -18,6 +18,18 @@ import { mergeDatabaseConfig } from './config';
 
 describe('config', () => {
   describe(mergeDatabaseConfig, () => {
+    it('does not mutate the input object', () => {
+      const input = {
+        original: 'key',
+      };
+      const override = {
+        added: 'value',
+      };
+
+      mergeDatabaseConfig(input, override);
+      expect(input).not.toHaveProperty('added');
+    });
+
     it('does not require overrides', () => {
       expect(
         mergeDatabaseConfig({