Use a jest.fn() to track calls to the scrubber, instead of a local variable counter

extensions/ql-vscode/src/query-history/query-history-scrubber.ts

@@ -10,10 +10,6 @@ import { getErrorMessage } from "../common/helpers-pure";
 
 const LAST_SCRUB_TIME_KEY = "lastScrubTime";
 
-type Counter = {
-  increment: () => void;
-};
-
 /**
  * Registers an interval timer that will periodically check for queries old enought
  * to be deleted.
@@ -37,8 +33,8 @@ export function registerQueryHistoryScrubber(
   qhm: QueryHistoryManager,
   ctx: ExtensionContext,
 
-  // optional counter to keep track of how many times the scrubber has run
-  counter?: Counter,
+  // optional callback to keep track of how many times the scrubber has run
+  onScrubberRun?: () => void,
 ): Disposable {
   const deregister = setInterval(
     scrubQueries,
@@ -48,7 +44,7 @@ export function registerQueryHistoryScrubber(
     queryHistoryDirs,
     qhm,
     ctx,
-    counter,
+    onScrubberRun,
   );
 
   return {
@@ -64,7 +60,7 @@ async function scrubQueries(
   queryHistoryDirs: QueryHistoryDirs,
   qhm: QueryHistoryManager,
   ctx: ExtensionContext,
-  counter?: Counter,
+  onScrubberRun?: () => void,
 ) {
   const lastScrubTime = ctx.globalState.get<number>(LAST_SCRUB_TIME_KEY);
   const now = Date.now();
@@ -76,7 +72,7 @@ async function scrubQueries(
 
     let scrubCount = 0; // total number of directories deleted
     try {
-      counter?.increment();
+      onScrubberRun?.();
       void extLogger.log(
         "Cleaning up query history directories. Removing old entries.",
       );

extensions/ql-vscode/test/vscode-tests/no-workspace/query-history/query-history-scrubber.test.ts

@@ -21,7 +21,6 @@ const LESS_THAN_ONE_DAY = ONE_DAY_IN_MS - 1000;
 
 describe("query history scrubber", () => {
   let deregister: vscode.Disposable | undefined;
-  let runCount = 0;
 
   const tmpDir = dirSync({
     unsafeCleanup: true,
@@ -45,27 +44,27 @@ describe("query history scrubber", () => {
 
   it("should not throw an error when the query directory does not exist", async () => {
     const mockCtx = createMockContext();
-    registerScrubber("idontexist", mockCtx);
+    const runCounter = registerScrubber("idontexist", mockCtx);
 
     jest.advanceTimersByTime(ONE_HOUR_IN_MS);
     await wait();
     // "Should not have called the scrubber"
-    expect(runCount).toBe(0);
+    expect(runCounter).toHaveBeenCalledTimes(0);
 
     jest.advanceTimersByTime(ONE_HOUR_IN_MS - 1);
     await wait();
     // "Should not have called the scrubber"
-    expect(runCount).toBe(0);
+    expect(runCounter).toHaveBeenCalledTimes(0);
 
     jest.advanceTimersByTime(1);
     await wait();
     // "Should have called the scrubber once"
-    expect(runCount).toBe(1);
+    expect(runCounter).toHaveBeenCalledTimes(1);
 
     jest.advanceTimersByTime(TWO_HOURS_IN_MS);
     await wait();
     // "Should have called the scrubber a second time"
-    expect(runCount).toBe(2);
+    expect(runCounter).toHaveBeenCalledTimes(2);
 
     expect((mockCtx.globalState as any).lastScrubTime).toBe(
       now + TWO_HOURS_IN_MS * 2,
@@ -178,7 +177,11 @@ describe("query history scrubber", () => {
     } as any as vscode.ExtensionContext;
   }
 
-  function registerScrubber(dir: string, ctx: vscode.ExtensionContext) {
+  function registerScrubber(
+    dir: string,
+    ctx: vscode.ExtensionContext,
+  ): jest.Mock {
+    const onScrubberRun = jest.fn();
     deregister = registerQueryHistoryScrubber(
       ONE_HOUR_IN_MS,
       TWO_HOURS_IN_MS,
@@ -190,10 +193,9 @@ describe("query history scrubber", () => {
         },
       }),
       ctx,
-      {
-        increment: () => runCount++,
-      },
+      onScrubberRun,
     );
+    return onScrubberRun;
   }
 
   async function wait(ms = 500) {