Fixes to decorator unit tests (microsoft#6047)

* Fixes to tests * Update comments * Fixes to tests

Author: DonJayamanne

src/test/common/utils/decorators.unit.test.ts

@@ -20,6 +20,7 @@ suite('Common Utils - Decorators', () => {
  /*
  * Time in milliseconds (from some arbitrary point in time for current process).
  * Don't use new Date().getTime() to calculate differences in times.
+ * Similarly setTimeout doesn't always trigger at prescribed time (accuracy isn't guaranteed).
  * This has an accuracy of around 2-20ms.
  * However we're dealing with tests that need accuracy of 1ms.
  * Use API that'll give us better accuracy when dealing with elapsed times.
@@ -31,6 +32,28 @@ suite('Common Utils - Decorators', () => {
  // Convert seconds to ms and nanoseconds to ms.
  return (currentTime[0] * 1000) + (currentTime[1] / 1000_000);
  }
+
+ /**
+ * setTimeout doesn't always trigger at prescribed time (accuracy isn't guaranteed).
+ * Allow a discrepancy of +-5%.
+ * Here's a simple test to prove this (this has been reported by others too):
+ * ```js
+ * // Execute the following around 100 times, you'll see at least one where elapsed time is < 100.
+ * const startTime = ....
+ * await new Promise(resolve = setTimeout(resolve, 100))
+ * console.log(currentTime - startTijme)
+ * ```
+ *
+ * @param {number} actualDelay
+ * @param {number} expectedDelay
+ */
+ function assertElapsedTimeWithinRange(actualDelay: number, expectedDelay: number) {
+ const difference = actualDelay - expectedDelay;
+ if (difference >= 0) {
+ return;
+ }
+ expect(Math.abs(difference)).to.be.lessThan(expectedDelay * 0.05, `Actual delay ${actualDelay}, expected delay ${expectedDelay}, not within 5% of accuracy`);
+ }
  function createMockVSC(pythonPath: string): typeof import('vscode') {
  return {
  workspace: {
@@ -162,7 +185,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  });
@@ -183,7 +206,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  expect(errored).to.be.equal(false, 'Exception raised when there shouldn\'t have been any');
@@ -204,7 +227,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  });
@@ -226,7 +249,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  expect(capturedEx).to.not.be.equal(undefined, 'Exception not re-thrown');
@@ -251,7 +274,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  expect(errored).to.be.equal(false, 'Exception raised when there shouldn\'t have been any');
@@ -273,7 +296,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  });
@@ -297,7 +320,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 2);
  const delay = one.timestamps[1] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run', 'run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  expect(errored).to.be.equal(false, 'Exception raised when there shouldn\'t have been any');
@@ -320,7 +343,7 @@ suite('Common Utils - Decorators', () => {
  await waitForCalls(one.timestamps, 1);
  const delay = one.timestamps[0] - start;
 
- expect(delay).to.be.at.least(wait);
+ assertElapsedTimeWithinRange(delay, wait);
  expect(one.calls).to.deep.equal(['run']);
  expect(one.timestamps).to.have.lengthOf(one.calls.length);
  });