Added screenshot of the RackUnit GUI, fixed typo.

rackunit-doc/rackunit/scribblings/control-flow.scrbl

@@ -7,7 +7,7 @@ The @racket[before], @racket[after], and @racket[around]
 macros allow you to specify code that is always run before,
 after, or around expressions in a test case.
 
-@defform[(before before-expr expr1 expr2 ...)]{
+@defform[(before before-expr expr-1 expr-2 ...)]{
 
 Whenever control enters the scope execute the @racket[before-expr]
 before executing @racket[expr-1], and @racket[expr-2 ...]}

rackunit-doc/rackunit/scribblings/ui.scrbl

@@ -47,6 +47,29 @@ GUI is updated as tests complete.
 
 When @racket[wait?] is true, @racket[test/gui] does not return until
 the test runner window has been closed.
+
+ Given the following program, the RackUnit GUI will look as shown below:
+
+ @racketblock[
+ #,(hash-lang) racket
+ (require rackunit rackunit/gui)
+ (test/gui
+  (test-suite
+   "all tests"
+   (test-suite
+    "math tests"
+    (test-case "addition" (check-equal? (+ 1 1) 2))
+    (test-case "subtraction" (check-equal? (- 0 0) 0))
+    (test-case "multiplication" (check-equal? (* 2 2) 5)))
+   (test-suite
+    "string tests"
+    (test-case "append" (check-equal? (string-append "a" "b") "ab"))
+    (test-case "ref" (check-equal? (string-ref "abc" 1) #\b)))))]
+
+ @image["scribblings/rackunit-screen-shot.png"]{Screenshot of the RackUnit
+  window. It features a tree representing the nested test suites (with test
+  cases as leaves) on the left pane, and information about the selected test
+  failure in the right pane.}
 }
 
 @defproc[(make-gui-runner)