fix: improve golden-layout test cleanup and fix replaceChild bug

- Make cleanupLayout() assert on destruction instead of swallowing errors
- Fix replaceChild event subscription bug by adding Tab.setContentItem()
  that properly transfers event listeners when content item changes
- Remove redundant explicit "destroys the layout" tests (afterEach now
  validates destruction after every test)
- Add migration plan documentation

Test count: 91 total (89 passing, 2 skipped popout tests)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dsmmcken

packages/golden-layout/plans/karma-to-jest-migration-plan.md

@@ -87,28 +87,4 @@ describe('emits events when components are created', () => {
     expect(eventListener.show).toHaveBeenCalledTimes(1);
     expect(eventListener.shown).toHaveBeenCalledTimes(1);
   });
-
-  it('destroys the layout', async () => {
-    layout = createTestLayout(
-      {
-        content: [
-          {
-            type: 'component',
-            componentName: 'testComponent',
-          },
-        ],
-      },
-      class {
-        constructor(cont: ItemContainer) {
-          cont.getElement().html('that worked');
-        }
-      }
-    );
-
-    layout.init();
-    await waitForLayoutInit(layout);
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/component-creation-events.test.ts

@@ -120,19 +120,4 @@ describe("Sets and retrieves a component's state", () => {
 
     expect(getComponentState(myLayout).testValue).toBe('updated');
   });
-
-  it('Destroys the layout', async () => {
-    myLayout = createTestLayout(
-      statefulConfig,
-      class {
-        constructor(cont: ItemContainer) {
-          cont.getElement().html('that worked');
-        }
-      }
-    );
-    await initLayout(myLayout);
-
-    myLayout.destroy();
-    expect(myLayout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/component-state-save.test.ts

@@ -229,18 +229,4 @@ describe('supports drag creation with deferred content', () => {
       restoreMocks();
     }
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/deferred-create-drag.test.ts

@@ -132,18 +132,4 @@ describe('selection is disabled by default', () => {
     expect(selectionChangedSpy).toHaveBeenCalledTimes(0);
     expect(layout.selectedItem).toBe(null);
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/disabled-selection.test.ts

@@ -229,18 +229,4 @@ describe('supports drag creation', () => {
       restoreMocks();
     }
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/drag.test.ts

@@ -110,28 +110,4 @@ describe('The layout can handle empty stacks', () => {
 
     expect(stack.contentItems.length).toBe(1);
   });
-
-  it('destroys the layout', async () => {
-    myLayout = await createLayout({
-      content: [
-        {
-          type: 'row',
-          content: [
-            {
-              type: 'component',
-              componentName: 'testComponent',
-            },
-            {
-              isClosable: false,
-              type: 'stack',
-              content: [],
-            },
-          ],
-        },
-      ],
-    });
-
-    myLayout.destroy();
-    expect(myLayout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/empty-item.test.ts

@@ -258,21 +258,4 @@ describe('selection works when enabled', () => {
     expect(stackA.element.hasClass('lm_selected')).toBe(true);
     expect(stackB.element.hasClass('lm_selected')).toBe(false);
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      settings: {
-        selectionEnabled: true,
-      },
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/enabled-selection.test.ts

@@ -194,18 +194,4 @@ describe('content items are abled to to emit events that bubble up the tree', ()
     expect(invocations[1]).toBe('stackBottom');
     expect(invocations[2]).toBe('column');
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });

packages/golden-layout/src/__tests__/event-bubble.test.ts

@@ -139,18 +139,4 @@ describe('Dynamic ids work properly', () => {
       item.removeId('non_existent_id');
     }).toThrow();
   });
-
-  it('destroys the layout', async () => {
-    layout = await createLayout({
-      content: [
-        {
-          type: 'component',
-          componentName: 'testComponent',
-        },
-      ],
-    });
-
-    layout.destroy();
-    expect(layout.root.contentItems.length).toBe(0);
-  });
 });