Rewrite ReactTreeTraversal-test.js using public APIs (#11664)

* rewrite two phase traversal tests with public APIs

* rewrite enter/leave tests

* lift render into beforeEach, organise variables

* move getLowestCommonAncestor test

* remove internal tree traversal test

* fix linter errors

* move creation of outer nodes into {before,after}Each

* explain why getLowestCommonAncestor test was moved

* remove unnessecary ARG and ARG2 token

these were used for testing the internal API to simulate synthetic
events passed to traverseEnterLeave. since we're now dealing with
actual synthetic events we can remove them.

* run prettier

packages/events/__tests__/ResponderEventPlugin-test.internal.js

@@ -1360,4 +1360,90 @@ describe('ResponderEventPlugin', () => {
     run(config, three, nativeEvent);
     expect(ResponderEventPlugin._getResponder()).toBe(null);
   });
+
+  it('should determine the first common ancestor correctly', () => {
+    // This test was moved here from the ReactTreeTraversal test since only the 
+    // ResponderEventPlugin uses `getLowestCommonAncestor`
+    var React = require('react');
+    var ReactTestUtils = require('react-dom/test-utils');
+    var ReactTreeTraversal = require('shared/ReactTreeTraversal');
+    var ReactDOMComponentTree = require('../../react-dom/src/client/ReactDOMComponentTree');
+
+    class ChildComponent extends React.Component {
+      render() {
+        return (
+          <div ref="DIV" id={this.props.id + '__DIV'}>
+            <div ref="DIV_1" id={this.props.id + '__DIV_1'} />
+            <div ref="DIV_2" id={this.props.id + '__DIV_2'} />
+          </div>
+        );
+      }
+    }
+
+    class ParentComponent extends React.Component {
+      render() {
+        return (
+          <div ref="P" id="P">
+            <div ref="P_P1" id="P_P1">
+              <ChildComponent ref="P_P1_C1" id="P_P1_C1" />
+              <ChildComponent ref="P_P1_C2" id="P_P1_C2" />
+            </div>
+            <div ref="P_OneOff" id="P_OneOff" />
+          </div>
+        );
+      }
+    }
+
+    var parent = ReactTestUtils.renderIntoDocument(<ParentComponent />);
+
+    var ancestors = [
+      // Common ancestor with self is self.
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_P1_C1.refs.DIV_1,
+        com: parent.refs.P_P1_C1.refs.DIV_1,
+      },
+      // Common ancestor with self is self - even if topmost DOM.
+      {one: parent.refs.P, two: parent.refs.P, com: parent.refs.P},
+      // Siblings
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_P1_C1.refs.DIV_2,
+        com: parent.refs.P_P1_C1.refs.DIV,
+      },
+      // Common ancestor with parent is the parent.
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_P1_C1.refs.DIV,
+        com: parent.refs.P_P1_C1.refs.DIV,
+      },
+      // Common ancestor with grandparent is the grandparent.
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_P1,
+        com: parent.refs.P_P1,
+      },
+      // Grandparent across subcomponent boundaries.
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_P1_C2.refs.DIV_1,
+        com: parent.refs.P_P1,
+      },
+      // Something deep with something one-off.
+      {
+        one: parent.refs.P_P1_C1.refs.DIV_1,
+        two: parent.refs.P_OneOff,
+        com: parent.refs.P,
+      },
+    ];
+    var i;
+    for (i = 0; i < ancestors.length; i++) {
+      var plan = ancestors[i];
+      var firstCommon = ReactTreeTraversal.getLowestCommonAncestor(
+        ReactDOMComponentTree.getInstanceFromNode(plan.one),
+        ReactDOMComponentTree.getInstanceFromNode(plan.two),
+      );
+      expect(firstCommon).toBe(ReactDOMComponentTree.getInstanceFromNode(plan.com));
+    }
+  });
 });