Testing memory leaks

[heyMP]

Here is an example of how you can test for memory leaks in our test runners:

test('attaching and removing the consumer should not leak', async () => {
    window.gc();
    const heap = performance.memory.usedJSHeapSize;
    for (let i = 0; i < 1000; i++) {
      // Remove the previous consumer & add a new one.
      consumer.remove();
      consumer = document.createElement(
        'context-consumer'
      ) as ContextConsumerElement;
      (consumer as any).heapExpandoProp = big();
      provider.appendChild(consumer);
      await consumer.updateComplete;
    }
    // Expect the nodes that were removed to be garbage collected.
    window.gc();
    // Allow a 50% margin of heap growth; due to the 10kb expando, an actual
    // DOM leak is orders of magnitude larger
    assert.isAtMost(
      performance.memory.usedJSHeapSize,
      heap * 1.5,
      'memory leak detected'
    );
  });

source: lit/lit@4f71df9#diff-83ddb0dcca4026e90703108749793b9aee6202e00eafb35dd143ffac81c64d95R196-R218

[bennypowers]

would make a nice contribution to @patternfly/create-element