Race Condition in the Test Engine When There are Multiple Files

When two files are running at the same time, their test results are mixed together.

Here is an example. In DrRacket, when I start A.rkt first and then run B.rkt while A is still running (or vice versa), their test results are mixed together. Depending on the launching order, the test result will even change.

A.rkt

;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname A) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f () #f)))

(check-expect "A.rkt-1" false)

(check-expect
 (begin
   (sleep 5)
   "A.rkt-2")
 false)

B.rkt

;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname B) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f () #f)))

(check-expect "B.rkt-1" "B.rkt-1")

(check-expect
 (begin
   (sleep 5)
   "B.rkt-2")
 "B.rkt-2")

Software version:

[May 10 16:44:16] $ racket -v
Welcome to Racket v8.1.0.4 [cs].
[May 10 16:44:45] $ raco pkg show htdp-lib drracket
Installation-wide:
 Package[*=auto]  Checksum              Source
 drracket*        75519974f33dd2da3...  catalog...h=drracket
 htdp-lib*        6d8926510bd48aaee...  catalog...h=htdp-lib
User-specific for installation "development":
 [none]

Reproduce the race with the provided A.rkt and B.rkt examples in DrRacket, starting both files while one is still running. The work is done when each file's test results remain separate and deterministic regardless of launch order.