test(cursor): repro #8235

test/helpers/cursor.eachAsync.test.js

@@ -0,0 +1,30 @@
+'use strict';
+
+const assert = require('assert');
+const eachAsync = require('../../lib/helpers/cursor/eachAsync');
+
+describe('eachAsync()', function() {
+  it('exhausts large cursor without parallel calls (gh-8235)', function() {
+    this.timeout(10000);
+
+    let numInProgress = 0;
+    let num = 0;
+    const max = 1000;
+    let processed = 0;
+
+    function next(cb) {
+      assert.equal(numInProgress, 0);
+      ++numInProgress;
+      setTimeout(function() {
+        --numInProgress;
+        if (num++ >= max) {
+          return cb(null, null);
+        }
+        cb(null, { name: `doc${num}` });
+      }, 0);
+    }
+
+    return eachAsync(next, () => Promise.resolve(++processed), { parallel: 8 }).
+      then(() => assert.equal(processed, max));
+  });
+});