Fix CustomOverlayContainer test failures

These tests were utilizing the Document object in ways that were not
perfectly isolated. While they had some cleanup logic, other tests may
manipulate the Document in such a way that make these tests fail. Fix
this by allowing tests to inject a node to search for instead of
defaulting to `document.body`. The `document.body` node is used in the
actual `_createContainer()` method.

PER-9864: CustomOverlayContainer test failure

src/app/dialog-cdk/custom-overlay-container.spec.ts

@@ -26,31 +26,26 @@ describe('CustomOverlayContainer', () => {
     expect(customOverlayContainer).toBeTruthy();
   });
 
-  describe('_createContainer', () => {
-    it('should append the container to pr-app-root if it exists', () => {
-      const mockAppRoot = document.createElement('pr-app-root');
-      document.body.appendChild(mockAppRoot);
+  it('should append the container to pr-app-root if it exists', () => {
+    const mockBodyNode = document.createElement('body');
+    const mockAppRoot = document.createElement('pr-app-root');
+    mockBodyNode.appendChild(mockAppRoot);
 
-      customOverlayContainer['_createContainer']();
+    customOverlayContainer.appendContainer(mockBodyNode);
 
-      const container = document.querySelector('.cdk-overlay-container');
+    const container = mockBodyNode.querySelector('.cdk-overlay-container');
 
-      expect(container).toBeTruthy();
-      expect(mockAppRoot.contains(container!)).toBeTrue();
-
-      mockAppRoot.remove();
-      container?.remove();
-    });
-
-    it('should append the container to document.body if pr-app-root does not exist', () => {
-      customOverlayContainer['_createContainer']();
+    expect(container).toBeTruthy();
+    expect(mockAppRoot.contains(container!)).toBeTrue();
+  });
 
-      const container = document.querySelector('.cdk-overlay-container');
+  it('should append the container to document.body if pr-app-root does not exist', () => {
+    const mockBodyNode = document.createElement('body');
+    customOverlayContainer.appendContainer(mockBodyNode);
 
-      expect(container).toBeTruthy();
-      expect(document.body.contains(container!)).toBeTrue();
+    const container = mockBodyNode.querySelector('.cdk-overlay-container');
 
-      container?.remove();
-    });
+    expect(container).toBeTruthy();
+    expect(mockBodyNode.contains(container!)).toBeTrue();
   });
 });

src/app/dialog-cdk/custom-overlay-container.ts

@@ -4,16 +4,16 @@ import { Injectable } from '@angular/core';
 
 @Injectable()
 export class CustomOverlayContainer extends OverlayContainer {
-  protected _createContainer(): void {
+  public appendContainer(node: Element): void {
     const container = document.createElement('div');
     container.classList.add('cdk-overlay-container');
 
-    const parent = document.querySelector('pr-app-root') || document.body;
-    if (parent) {
-      parent.appendChild(container);
-    } else {
-      document.body.appendChild(container);
-    }
+    const parent = node.querySelector('pr-app-root') || node;
+    parent.appendChild(container);
     this._containerElement = container;
   }
+
+  protected _createContainer(): void {
+    this.appendContainer(document.body);
+  }
 }