There are a number of error paths in benchRun() that throw exceptions (e.g. if the request was malformed, if the "expected" option to find did not match the size of the query result set). By default, these exceptions cause the worker thread to terminate early; however, no error is reported in the result of the benchRun() call.

For example, the following script terminates the worker thread early (because the size of the query result set does not match the expected value), and shows that the benchRun() call returns success and that the "errCount" value is unchanged:

db.foo.drop();
var res = benchRun({ops: [{op: "find", query: {}, ns:"test.foo", expected: NumberInt(1)}], seconds: 3});
assert.gt(res.errCount, 0);  // Unexpected: does not trip.