fix(mock-doc): handle children in contains() (#3363)

update implementation for `contains()` to return `true` for
a depth of greater than one (when a node is indeed a descendant
of another)

src/mock-doc/node.ts

@@ -141,7 +141,12 @@ export class MockNode {
     if (otherNode === this) {
       return true;
     }
-    return this.childNodes.includes(otherNode);
+    const childNodes = Array.from(this.childNodes);
+    if (childNodes.includes(otherNode)) {
+      return true;
+    }
+
+    return childNodes.some((node) => this.contains.bind(node)(otherNode));
   }
 
   removeChild(childNode: MockNode) {

src/mock-doc/test/element.spec.ts

@@ -238,6 +238,39 @@ describe('element', () => {
     });
   });
 
+  describe('contains', () => {
+    it('returns true when a node is an direct child of a given node', () => {
+      const root = document.createElement('div');
+      const span = document.createElement('span');
+
+      root.appendChild(span);
+
+      expect(root.contains(span)).toEqual(true);
+    });
+
+    it('returns true when a node is an indirect child of a given node', () => {
+      const root = document.createElement('div');
+      const span = document.createElement('span');
+      const h1 = document.createElement('h1');
+
+      root.appendChild(span);
+      span.appendChild(h1);
+
+      expect(root.contains(h1)).toEqual(true);
+    });
+
+    it('returns true when a node is the given node itself', () => {
+      const root = document.createElement('div');
+      expect(root.contains(root)).toEqual(true);
+    });
+
+    it('returns false when a node is not the given node itself or not a descendant of the given node ', () => {
+      const root = document.createElement('div');
+      const span = document.createElement('span');
+      expect(root.contains(span)).toEqual(false);
+    });
+  });
+
   describe('isConnected', () => {
     it('nested true', () => {
       const elmParent = document.createElement('div');