test(OpenGLRenderWindow): regression for WebGL context leak

Mounts and unmounts the component 17 times - one past Chrome's
per-process WebGL context limit of 16 - and asserts that the cleanup
callback (a) calls WEBGL_lose_context.loseContext() once per cycle and
(b) does so strictly before view.delete(), so the GPU slot is returned
to the browser before vtk.js tears down the extension handle. Fails on
this commit; the fix lands next.

Author: sankhesh

src/__tests__/OpenGLRenderWindow.test.tsx

@@ -0,0 +1,130 @@
+/**
+ * Regression test: OpenGLRenderWindow must call WEBGL_lose_context.loseContext()
+ * during cleanup so that GPU slots are freed before Chrome's per-process
+ * WebGL context limit (~16) is reached.
+ *
+ * The test mounts and fully unmounts the component 17 times and asserts that
+ * loseContext() was called exactly once per lifecycle, proving that the GPU
+ * slot is returned to the browser on every destruction.
+ */
+
+import { cleanup, render } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+// Import the component before vi.mock() in source order.
+// Vitest hoists vi.mock() calls above all imports at transform time,
+// so the mock is always in place when the module is evaluated.
+import OpenGLRenderWindow from '../core/OpenGLRenderWindow';
+
+// ---------------------------------------------------------------------------
+// Hoisted mock state
+// vi.mock() is hoisted above all imports by Vitest, so any values the factory
+// closes over must be initialised with vi.hoisted() to avoid a TDZ error.
+// ---------------------------------------------------------------------------
+
+const { mockLoseContext, mockGetContext, mockNewInstance } = vi.hoisted(() => {
+  const mockLoseContext = vi.fn();
+
+  const mockGetExtension = vi.fn((name: string) =>
+    name === 'WEBGL_lose_context' ? { loseContext: mockLoseContext } : null
+  );
+
+  const mockGetContext = vi.fn(() => ({
+    getExtension: mockGetExtension,
+  }));
+
+  let instanceId = 0;
+  const mockNewInstance = vi.fn(() => ({
+    __id: ++instanceId,
+    setContainer: vi.fn(),
+    getCanvas: vi.fn(() => ({ getContext: mockGetContext })),
+    delete: vi.fn(),
+  }));
+
+  return { mockLoseContext, mockGetContext, mockNewInstance };
+});
+
+// ---------------------------------------------------------------------------
+// Module mock — must be declared at the top level for Vitest hoisting.
+// ---------------------------------------------------------------------------
+
+vi.mock('@kitware/vtk.js/Rendering/OpenGL/RenderWindow', () => ({
+  default: { newInstance: mockNewInstance },
+}));
+
+// ---------------------------------------------------------------------------
+// Helper
+// ---------------------------------------------------------------------------
+
+/**
+ * Render one <OpenGLRenderWindow>, then immediately unmount it.
+ * @testing-library wraps both calls in act(), so all useEffect cleanups
+ * (including the DeletionRegistry callback) are flushed synchronously before
+ * this function returns.
+ */
+function mountAndUnmount() {
+  const { unmount } = render(<OpenGLRenderWindow />);
+  unmount();
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('OpenGLRenderWindow – WebGL context lifecycle', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    cleanup();
+  });
+
+  it('calls loseContext() once per mount-unmount cycle across 17 cycles', () => {
+    // 17 is one past Chrome's hard per-process WebGL context limit of 16.
+    // Before the fix, the 17th context was never released, blanking the viewport.
+    const CYCLES = 17;
+
+    for (let i = 0; i < CYCLES; i++) {
+      mountAndUnmount();
+    }
+
+    expect(mockLoseContext).toHaveBeenCalledTimes(CYCLES);
+  });
+
+  it('calls loseContext() strictly before view.delete()', () => {
+    // Verify ordering: the GPU slot must be relinquished before vtk.js tears
+    // down its internal state, otherwise the extension handle is invalid.
+    const callOrder: string[] = [];
+
+    mockLoseContext.mockImplementationOnce(() => callOrder.push('loseContext'));
+
+    // Intercept delete() on whichever instance newInstance() creates next.
+    const nextInstance = {
+      __id: 999,
+      setContainer: vi.fn(),
+      getCanvas: vi.fn(() => ({ getContext: mockGetContext })),
+      delete: vi.fn(() => callOrder.push('delete')),
+    };
+    mockNewInstance.mockReturnValueOnce(nextInstance);
+
+    mountAndUnmount();
+
+    expect(callOrder).toEqual(['loseContext', 'delete']);
+  });
+
+  it('does not throw when getCanvas() is unavailable', () => {
+    // Guard against vtk.js builds where getCanvas() does not exist, e.g.
+    // server-side rendering stubs.  Cleanup must still succeed.
+    const instanceWithoutCanvas = {
+      __id: 1000,
+      setContainer: vi.fn(),
+      getCanvas: undefined, // no canvas accessor
+      delete: vi.fn(),
+    };
+    mockNewInstance.mockReturnValueOnce(instanceWithoutCanvas as never);
+
+    expect(() => mountAndUnmount()).not.toThrow();
+    expect(instanceWithoutCanvas.delete).toHaveBeenCalledOnce();
+  });
+});