enzyme components must exist

src/toHaveStyleRule.js

@@ -12,7 +12,7 @@ const getClassNames = received => {
   if (received) {
     if (received.$$typeof === Symbol.for('react.test.json')) {
       className = received.props.className || received.props.class
-    } else if (typeof received.findWhere === 'function') {
+    } else if (typeof received.exists === 'function' && received.exists()) {
       const tree = shouldDive(received) ? received.dive() : received
       const components = tree.findWhere(isTagWithClassName)
       if (components.length) {

test/__snapshots__/toHaveStyleRule.spec.js.snap

@@ -24,3 +24,5 @@ Expected
 Received:
   \\"background: orange\\""
 `;
+
+exports[`non existing 1`] = `"No style rules found on passed Component"`;

test/toHaveStyleRule.spec.js

@@ -91,6 +91,20 @@ test('message when value does not match', () => {
   }).toThrowErrorMatchingSnapshot()
 })
 
+test('non existing', () => {
+  const Wrapper = styled.section`
+    padding: 4em;
+    background: papayawhip;
+  `
+
+  expect(() => {
+    expect(shallow(<Wrapper />).find('div')).toHaveStyleRule(
+      'background',
+      'papayawhip'
+    )
+  }).toThrowErrorMatchingSnapshot()
+})
+
 test('basic', () => {
   const Wrapper = styled.section`
     padding: 4em;