Small changes/fixes to rackunit.

* Add optional message for fail-check.
* Correctly shorten column name.

pkgs/rackunit-pkgs/rackunit-doc/rackunit/scribblings/check.scrbl

@@ -419,10 +419,12 @@ if the macro @racket[fail-check] is called in the body of
 the check.  This allows more flexible checks, and in
 particular more flexible reporting options.}
 
-@defform[(fail-check)]{
+@defform*[[(fail-check)
+           (fail-check message-expr)]]{
 
 The @racket[fail-check] macro raises an @racket[exn:test:check] with
-the contents of the check information stack.
+the contents of the check information stack. The optional message
+is used as the exception's message.
 
 }
 

pkgs/rackunit-pkgs/rackunit-lib/rackunit/private/check.rkt

@@ -70,14 +70,19 @@
 
 (define-syntax fail-check
   (syntax-rules ()
-    ((_)
-     (let ([marks (current-continuation-marks)])
+    ((_ message*)
+     (let ([message message*]
+           [marks (current-continuation-marks)])
+       (unless (string? message)
+         (raise-type-error 'fail-check "string" message))
        (test-log! #f)
        (raise
         (make-exn:test:check
-         "Check failure"
+         message
          marks
-         (check-info-stack marks)))))))
+         (check-info-stack marks)))))
+    ((_)
+     (fail-check "Check failure"))))
 
 (define-syntax fail-internal
   (syntax-rules ()

pkgs/rackunit-pkgs/rackunit-lib/rackunit/private/format.rkt

@@ -37,7 +37,7 @@
    [(m . < . n)
     (string-append s (make-string (- n m) #\space))]
    [else
-    (substring s n)]))
+    (substring s 0 n)]))
 
 (define (display-check-info-name-value name value [value-printer write])
   (display (string-pad-right