Fixes of the core tests for testing on Windows

* Initialize the environment variables with paths to
  MSVC toolchain before running the racket-test-core,
  since the foreign library tests need a C compiler.

* Fix a bug in foreign-test.rktl that deletes the existing
  content of environment variables (PATH, INCLUDE, LIB, etc)

* Let a test in date.rktl fail more gracefully.

.github/workflows/ci_win.yml

@@ -47,7 +47,9 @@ jobs:
         call racket\raco.exe pkg install --auto --no-docs racket-test unstable-flonum-lib net-test
     - name: Run tests/racket/test
       shell: cmd
-      run: racket\raco.exe test -l tests/racket/test
+      run: |
+        call .\racket\src\worksp\msvcprep.bat x86_amd64
+        racket\raco.exe test -l tests/racket/test
     - name: Run tests/racket/contract/all
       shell: cmd
       run: racket\racket.exe -l tests/racket/contract/all

pkgs/racket-test-core/tests/racket/date.rktl

@@ -26,7 +26,9 @@
 (test 0 find-seconds 0 0 0 1 1 1970 #f)
 (test 32416215 find-seconds 15 30 4 11 1 1971 #f)
 
-(test 1969 date-year (seconds->date (- (* 24 60 60))))
+(define (date-year.seconds->date sec)
+  (date-year (seconds->date sec)))
+(test 1969 date-year.seconds->date (- (* 24 60 60)))
 
 (let* ([s (current-seconds)]
        [d1 (seconds->date s)]

pkgs/racket-test-core/tests/racket/foreign-test.rktl

@@ -73,17 +73,19 @@
     (and progfiles (concat progfiles "/Microsoft Visual Studio 10.0")))
   (when (and studio (directory-exists? studio))
     (define (paths-env var . ps)
+      (define orig-val (getenv var))
       (define val
         (apply concat (for/list ([p (in-list ps)]
                                  #:when (and p (directory-exists? p)))
                         (concat p ";"))))
       (printf ">>> $~a = ~s\n" var val)
-      (putenv var val))
+      (putenv var (if orig-val
+                      (concat orig-val ";" val)
+                      val)))
     (define (vc p)     (concat studio "/VC/" p))
     (define (common p) (concat studio "/Common7/" p))
     (define (winsdk p) (concat progfiles "/Microsoft SDKs/Windows/v7.0A/" p))
     (paths-env "PATH"
-               (getenv "PATH")
                (vc (if 64bit? "BIN/amd64" "BIN"))
                (vc "IDE") (vc "Tools") (vc "Tools/bin")
                (common "Tools") (common "IDE"))