Add counter example; fix configuration

examples/accident-counter/src/reducer.test.js

@@ -0,0 +1,29 @@
+import { describe, it, expect } from 'vitest';
+import { reducer } from './reducer';
+
+describe('reducer', () => {
+  it('should return the initial state', () => {
+    const initialState = { count: 0 };
+    expect(reducer()).toEqual(initialState);
+  });
+
+  it('should handle decrement action', () => {
+    const initialState = { count: 0 };
+    const action = { type: 'increment' };
+    const expectedState = { count: 1 };
+    expect(reducer(initialState, action)).toEqual(expectedState);
+  });
+
+  it('should handle increment action', () => {
+    const initialState = { count: 1 };
+    const action = { type: 'decrement' };
+    const expectedState = { count: 0 };
+    expect(reducer(initialState, action)).toEqual(expectedState);
+  });
+
+  it('should handle unknown action', () => {
+    const initialState = { count: 0 };
+    const action = { type: 'UNKNOWN' };
+    expect(reducer(initialState, action)).toEqual(initialState);
+  });
+});