Moar attribute tests (facebook#10509)

* WIP

* WIP Add the rest of the tests for what we expect re: unknown attributes

**what is the change?:**
Adds tests for the following behavior -

- Numbers and booleans should be converted to strings, and not warn
- NaN, Symbols, functions, and objects should be converted to strings,
  and *should* warn

Going to add tests for the not-warning behavior in a follow-up.

These tests are not entirely passing - we either need to change what we
expect or change the behavior.

**why make this change?:**
Gets everyone on the same page about expected behavior, and codifies it
in a maintainable way

**test plan:**
`yarn test src/renderers/dom/shared/__tests__/ReactDOMAttribute-test.js`

**issue:**
facebook#10399

* WIP Add check that we *don't* warn when handling some unknown attributes

**what is the change?:**
We are testing the behavior of unknown attributes, which has changed
since React 15.

We want to *not* warn for the following cases -
- null
- undefined
- missing
- strings
- numbers
- booleans

**why make this change?:**
We want to verify that warnings don't get fired at the wrong time.

**test plan:**
`yarn test src/renderers/dom/shared/__tests__/ReactDOMAttribute-test.js`

**issue:**
facebook#10399

* ran prettier

* Symbols and functions passed to unknown attributes should remove and warn

* Abstract tests a bit to make them easier to read

* Remove Markdown from test names

I don't think we use this convention anywhere.

* Add an assertion for NaN warning message

* Update ReactDOMAttribute test based on attribute fixture

**what is the change?:**
- booleans don't get stringified
- some warnings have changed since we originally wrote this

**why make this change?:**
The attribute behavior is finalized and now we can test it :D

I also found it handy to have a row with a truly unknown attribute, so
added "imaginaryFriend".

**test plan:**
`yarn test src/renderers/dom/shared/__tests__/ReactDOMAttribute-test.js`
and comparing the tests to the attribute table

**issue:**
facebook#10399

* remove imaginaryFriend to resolve conflict

* ran prettier

src/renderers/dom/shared/__tests__/ReactDOMAttribute-test.js

@@ -0,0 +1,137 @@
+/**
+ * Copyright 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+describe('ReactDOM unknown attribute', () => {
+  var React;
+  var ReactDOM;
+
+  beforeEach(() => {
+    jest.resetModules();
+    React = require('react');
+    ReactDOM = require('react-dom');
+  });
+
+  function normalizeCodeLocInfo(str) {
+    return str && str.replace(/\(at .+?:\d+\)/g, '(at **)');
+  }
+
+  function testUnknownAttributeRemoval(givenValue) {
+    var el = document.createElement('div');
+    ReactDOM.render(<div unknown="something" />, el);
+    expect(el.firstChild.getAttribute('unknown')).toBe('something');
+    ReactDOM.render(<div unknown={givenValue} />, el);
+    expect(el.firstChild.hasAttribute('unknown')).toBe(false);
+  }
+
+  function testUnknownAttributeAssignment(givenValue, expectedDOMValue) {
+    var el = document.createElement('div');
+    ReactDOM.render(<div unknown="something" />, el);
+    expect(el.firstChild.getAttribute('unknown')).toBe('something');
+    ReactDOM.render(<div unknown={givenValue} />, el);
+    expect(el.firstChild.getAttribute('unknown')).toBe(expectedDOMValue);
+  }
+
+  describe('unknown attributes', () => {
+    it('removes values null and undefined', () => {
+      testUnknownAttributeRemoval(null);
+      testUnknownAttributeRemoval(undefined);
+    });
+
+    it('changes values true, false to null, and also warns once', () => {
+      spyOn(console, 'error');
+
+      testUnknownAttributeAssignment(true, null);
+      testUnknownAttributeAssignment(false, null);
+
+      expectDev(
+        normalizeCodeLocInfo(console.error.calls.argsFor(0)[0]),
+      ).toMatch(
+        'Warning: Received `true` for non-boolean attribute `unknown`. ' +
+          'If this is expected, cast the value to a string.\n' +
+          '    in div (at **)',
+      );
+      expectDev(console.error.calls.count()).toBe(1);
+    });
+
+    it('removes unknown attributes that were rendered but are now missing', () => {
+      var el = document.createElement('div');
+      ReactDOM.render(<div unknown="something" />, el);
+      expect(el.firstChild.getAttribute('unknown')).toBe('something');
+      ReactDOM.render(<div />, el);
+      expect(el.firstChild.hasAttribute('unknown')).toBe(false);
+    });
+
+    it('passes through strings', () => {
+      testUnknownAttributeAssignment('a string', 'a string');
+    });
+
+    it('coerces numbers to strings', () => {
+      testUnknownAttributeAssignment(0, '0');
+      testUnknownAttributeAssignment(-1, '-1');
+      testUnknownAttributeAssignment(42, '42');
+      testUnknownAttributeAssignment(9000.99, '9000.99');
+    });
+
+    it('coerces NaN to strings and warns', () => {
+      spyOn(console, 'error');
+
+      testUnknownAttributeAssignment(NaN, 'NaN');
+      expectDev(
+        normalizeCodeLocInfo(console.error.calls.argsFor(0)[0]),
+      ).toMatch(
+        'Warning: Received NaN for numeric attribute `unknown`. ' +
+          'If this is expected, cast the value to a string.\n' +
+          '    in div (at **)',
+      );
+      expectDev(console.error.calls.count()).toBe(1);
+    });
+
+    it('coerces objects to strings **and warns**', () => {
+      const lol = {
+        toString() {
+          return 'lol';
+        },
+      };
+
+      testUnknownAttributeAssignment({hello: 'world'}, '[object Object]');
+      testUnknownAttributeAssignment(lol, 'lol');
+    });
+
+    it('removes symbols and warns', () => {
+      spyOn(console, 'error');
+
+      testUnknownAttributeRemoval(Symbol('foo'));
+      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
+        'Warning: Invalid prop `unknown` on <div> tag. Either remove this ' +
+          'prop from the element, or pass a string or number value to keep it ' +
+          'in the DOM. For details, see https://fb.me/react-unknown-prop\n' +
+          '    in div (at **)',
+      );
+      expectDev(console.error.calls.count()).toBe(1);
+    });
+
+    it('removes functions and warns', () => {
+      spyOn(console, 'error');
+
+      testUnknownAttributeRemoval(function someFunction() {});
+      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(
+        'Warning: Invalid prop `unknown` on <div> tag. Either remove this ' +
+          'prop from the element, or pass a string or number value to ' +
+          'keep it in the DOM. For details, see ' +
+          'https://fb.me/react-unknown-prop\n' +
+          '    in div (at **)',
+      );
+      expectDev(console.error.calls.count()).toBe(1);
+    });
+  });
+});