Update some of the exercises

examples/basic-math/src/counter.test.js

@@ -0,0 +1,21 @@
+import { expect, it, describe } from 'vitest';
+import { counter } from './counter';
+
+// For added fun, we can try `describe.shuffle`.
+describe.todo('Counter', () => {
+  it('starts at zero', () => {
+    expect(counter.value).toBe(0);
+  });
+
+  it('can increment', () => {
+    counter.increment();
+    expect(counter.value).toBe(1);
+  });
+
+  // Let's get this test to *not* fail.
+  it('can decrement', () => {
+    counter.increment();
+    counter.decrement();
+    expect(counter.value).toBe(0);
+  });
+});