[test-stress-options] Set COMBINATORICS to full path to jenny

Setting COMBINATORICS to the full path name to jenny will enable
pairwise testing.

e.g. COMBINATORICS=/home/user/jenny/jenny ninja check

gnucash/report/standard-reports/test/test-stress-options.scm

@@ -17,6 +17,15 @@
 (use-modules (sxml simple))
 (use-modules (sxml xpath))
 
+;; NOTE
+;; ----
+;; SIMPLE stress tests by default
+;;
+;; PAIRWISE COMBINATORICS are enabled by setting environment variable COMBINATORICS
+;; to the fullpath for the compiled jenny from http://burtleburtle.net/bob/math/jenny.html
+;;
+;; e.g. COMBINATORICS=/home/user/jenny/jenny ninja check
+
 (load "test-stress-optionslist.scm")
 ;; The above optionslist was generated programmatically.  It was
 ;; generated by running a sentinel function in the middle of an
@@ -81,6 +90,18 @@
   (tests)
   (test-end "stress options"))
 
+(define jennypath
+  (get-environment-variable "COMBINATORICS"))
+
+(define jenny-exists?
+  ;; this is a simple test for presence of jenny - will check
+  ;; COMBINATORICS env exists, and running it produces exit-code of
+  ;; zero, and tests the first few letters of its output.
+  (and (string? jennypath)
+       (zero? (system jennypath))
+       (string=? (string-take (get-string-all (open-input-pipe jennypath)) 6)
+                 "jenny:")))
+
 (define (set-option! options section name value)
   (let ((option (gnc:lookup-option options section name)))
     (if option
@@ -175,8 +196,8 @@
                            ;; the following is the n-tuple
                            2
                            (length report-options)))
-                 (cmdline (format #f "/home/chris/sources/jenny/jenny -n~a ~a"
-                                  n-tuple jennyargs))
+                 (cmdline (format #f "~a -n~a ~a"
+                                  jennypath n-tuple jennyargs))
                  (jennyout (get-string-all (open-input-pipe cmdline)))
                  (test-cases (string-split jennyout #\newline)))
             (for-each
@@ -221,7 +242,7 @@
   ;; what strategy are we using here? simple stress test (ie tests as
   ;; many times as the maximum number of options) or combinatorial
   ;; tests (using jenny)
-  (if (get-environment-variable "COMBINATORICS")
+  (if jenny-exists?
       combinatorial-stress-test
       simple-stress-test))