Allow debug() to accept a parameter

src/vue-testing-library.js

@@ -64,7 +64,7 @@ function render (TestComponent, {
   return {
     container: wrapper.element.parentNode,
     baseElement: document.body,
-    debug: () => console.log(prettyDOM(wrapper.element)),
+    debug: (el = wrapper.element) => console.log(prettyDOM(el)),
     unmount: () => wrapper.destroy(),
     isUnmounted: () => wrapper.vm._isDestroyed,
     html: () => wrapper.html(),

tests/__tests__/components/HelloWorld.vue

@@ -1,3 +1,6 @@
 <template>
-  <div>Hello World!</div>
+  <div>
+    <h1>Hello World!</h1>
+    <p>Lorem ipsum dolor sit amet</p>
+  </div>
 </template>

tests/__tests__/debug.js

@@ -10,11 +10,33 @@ afterEach(() => {
   console.log.mockRestore()
 })
 
-test('debug pretty prints the container', () => {
+test('debug pretty prints the container if no parameter is provided', () => {
   const { debug } = render(HelloWorld)
+
   debug()
+
+  expect(console.log).toHaveBeenCalledTimes(1)
+  expect(console.log).toHaveBeenCalledWith(
+    expect.stringContaining('Hello World')
+  )
+  expect(console.log).toHaveBeenCalledWith(
+    expect.stringContaining('Lorem ipsum dolor sit amet')
+  )
+})
+
+test('debug pretty prints the provided parameter', () => {
+  const { getByText, debug } = render(HelloWorld)
+
+  // debug accepts a DOM node as a parameter.
+  debug(getByText('Lorem ipsum dolor sit amet'))
+
   expect(console.log).toHaveBeenCalledTimes(1)
   expect(console.log).toHaveBeenCalledWith(
+    expect.stringContaining('Lorem ipsum dolor sit amet')
+  )
+
+  // Notice the 'not' particle
+  expect(console.log).not.toHaveBeenCalledWith(
     expect.stringContaining('Hello World')
   )
 })