timerate: added test illustrating drastic growth of execution time on iteration with quadratic complexity

1 files changed, 20 insertions, 1 deletions

diff --git a/tests/cmdMZ.test b/tests/cmdMZ.test
index 028a71b..d9f4282 100644
--- a/tests/cmdMZ.test
+++ b/tests/cmdMZ.test
@@ -487,7 +487,26 @@ test cmdMZ-6.12 {Tcl_TimeRateObjCmd: done optimization: nested call of self insi
     }
     list [lindex [timerate $m1 1000 5] 2] $x
 } {5 20}
-
+test cmdMZ-6.13 {Tcl_TimeRateObjCmd: stability by O(n**2), avoid long execution time on growing iteration time} {
+    set result {}
+    # test the function with quadratic complexity (iteration growth 2x, 10x, 100x):
+    foreach e {2 10 100} {
+	set x 1
+	set m1 [timerate {
+	    apply {x {
+		while {[incr x -1]} {}
+	    }} [set x [expr {$x*$e}]]
+	} 50]
+	lappend result "${e}x"
+	# check it was too slow (it is OK to use factor 2 to prevent sporadic
+	# errors on some slow systems or time issues, because if it is not fixed,
+	# the execution time may grow hundreds and thousand times):
+	if {[lindex $m1 6] > 50 * 2} {
+	    lappend result "unexpected long: $m1"
+	}
+    }
+    set result
+} {2x 10x 100x}
 # The tests for Tcl_WhileObjCmd are in while.test
 
 # cleanup