diff --git a/src/editor/reducers.test.ts b/src/editor/reducers.test.ts
new file mode 100644
index 00000000..b53531bc
--- /dev/null
+++ b/src/editor/reducers.test.ts
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2021 The Pybricks Authors
+
+import { Ace } from 'ace-builds';
+import { Action } from '../actions';
+import { setEditSession } from './actions';
+import reducers from './reducers';
+
+type State = ReturnType<typeof reducers>;
+
+test('initial state', () => {
+    expect(reducers(undefined, {} as Action)).toMatchInlineSnapshot(`
+        Object {
+          "current": null,
+        }
+    `);
+});
+
+test('current', () => {
+    const session = {} as Ace.EditSession;
+    expect(reducers({ current: null } as State, setEditSession(session)).current).toBe(
+        session,
+    );
+    expect(
+        reducers({ current: session } as State, setEditSession(undefined)).current,
+    ).toBe(null);
+});