add crossing_way validation

Tests are also added and passed.

One thing to note: I had to add the tree() function to history so that I can
use the tree in the test; hope that's fine.

test/index.html

@@ -144,6 +144,7 @@
     <script src='spec/util/util.js'></script>
 
     <script src='spec/validations/missing_tag.js'></script>
+    <script src='spec/validations/crossing_ways.js'></script>
     <script src='spec/operations/detach_node.js'></script>
     <script>
         window.mocha.run();

test/spec/validations/crossing_ways.js

@@ -0,0 +1,106 @@
+describe('iD.validations.crossing_ways', function () {
+    var context;
+
+    beforeEach(function() {
+        context = iD.Context();
+    });
+
+    function createWaysWithOneCrossingPoint() {
+        var n1 = iD.Node({id: 'n-1', loc: [1,1]});
+        var n2 = iD.Node({id: 'n-2', loc: [2,2]});
+        var w1 = iD.Way({id: 'w-1', nodes: ['n-1', 'n-2'], tags: { highway: 'residential' }});
+
+        context.perform(
+            iD.actionAddEntity(n1),
+            iD.actionAddEntity(n2),
+            iD.actionAddEntity(w1)
+        );
+
+        var n3 = iD.Node({id: 'n-3', loc: [1,2]});
+        var n4 = iD.Node({id: 'n-4', loc: [2,1]});
+        var w2 = iD.Way({id: 'w-2', nodes: ['n-3', 'n-4'], tags: { highway: 'residential' }});
+
+        context.perform(
+            iD.actionAddEntity(n3),
+            iD.actionAddEntity(n4),
+            iD.actionAddEntity(w2)
+        );
+    }
+
+    function createWaysWithTwoCrossingPoint() {
+      var n1 = iD.Node({id: 'n-1', loc: [1,1]});
+      var n2 = iD.Node({id: 'n-2', loc: [3,3]});
+      var w1 = iD.Way({id: 'w-1', nodes: ['n-1', 'n-2'], tags: { highway: 'residential' }});
+
+      context.perform(
+          iD.actionAddEntity(n1),
+          iD.actionAddEntity(n2),
+          iD.actionAddEntity(w1)
+      );
+
+      var n3 = iD.Node({id: 'n-3', loc: [1,2]});
+      var n4 = iD.Node({id: 'n-4', loc: [2,1]});
+      var n5 = iD.Node({id: 'n-5', loc: [3,2]});
+      var n6 = iD.Node({id: 'n-6', loc: [2,3]});
+      var w2 = iD.Way({id: 'w-2', nodes: ['n-3', 'n-4', 'n-5', 'n-6'], tags: { highway: 'residential' }});
+
+      context.perform(
+          iD.actionAddEntity(n3),
+          iD.actionAddEntity(n4),
+          iD.actionAddEntity(n5),
+          iD.actionAddEntity(n6),
+          iD.actionAddEntity(w2)
+      );
+    }
+
+    function validate() {
+        var validator = iD.validationHighwayCrossingOtherWays();
+        var changes = context.history().changes();
+        return validator(changes, context.graph(), context.history().tree());
+    }
+
+    it('has no errors on init', function() {
+        var issues = validate();
+        expect(issues).to.have.lengthOf(0);
+    });
+
+    it('one cross point between two ways', function() {
+        createWaysWithOneCrossingPoint();
+        var issues = validate();
+        expect(issues).to.have.lengthOf(1);
+        var issue = issues[0];
+        expect(issue.type).to.eql(iD.ValidationIssueType.crossing_ways);
+        expect(issue.entities).to.have.lengthOf(2);
+        expect(issue.entities[0].id).to.eql('w-1');
+        expect(issue.entities[1].id).to.eql('w-2');
+
+        expect(issue.coordinates).to.have.lengthOf(2);
+        expect(issue.coordinates[0]).to.eql(1.5);
+        expect(issue.coordinates[1]).to.eql(1.5);
+    });
+
+    it('two cross points between two ways', function() {
+        createWaysWithTwoCrossingPoint();
+        var issues = validate();
+        expect(issues).to.have.lengthOf(2);
+        var issue = issues[0];
+        expect(issue.type).to.eql(iD.ValidationIssueType.crossing_ways);
+        expect(issue.entities).to.have.lengthOf(2);
+        expect(issue.entities[0].id).to.eql('w-1');
+        expect(issue.entities[1].id).to.eql('w-2');
+
+        expect(issue.coordinates).to.have.lengthOf(2);
+        expect(issue.coordinates[0]).to.eql(1.5);
+        expect(issue.coordinates[1]).to.eql(1.5);
+
+        issue = issues[1];
+        expect(issue.type).to.eql(iD.ValidationIssueType.crossing_ways);
+        expect(issue.entities).to.have.lengthOf(2);
+        expect(issue.entities[0].id).to.eql('w-1');
+        expect(issue.entities[1].id).to.eql('w-2');
+
+        expect(issue.coordinates).to.have.lengthOf(2);
+        expect(issue.coordinates[0]).to.eql(2.5);
+        expect(issue.coordinates[1]).to.eql(2.5);
+    });
+});