diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 2ff124b..fdac405 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2473,6 +2473,7 @@
 test_null_list()		List	null value for testing
 test_null_partial()		Funcref	null value for testing
 test_null_string()		String	null value for testing
+test_option_not_set({name})    none	reset flag indicating option was set
 test_override({expr}, {val})    none	test with Vim internal overrides
 test_settime({expr})		none	set current time for testing
 timer_info([{id}])		List	information about timers
@@ -8737,6 +8738,15 @@
 test_null_string()					*test_null_string()*
 		Return a String that is null. Only useful for testing.
 
+test_option_not_set({name})				*test_option_not_set()*
+		Reset the flag that indicates option {name} was set.  Thus it
+		looks like it still has the default value. Use like this: >
+			set ambiwidth=double
+			call test_option_not_set('ambiwidth')
+<		Now the 'ambiwidth' option behaves like it was never changed,
+		even though the value is "double".
+		Only to be used for testing!
+
 test_override({name}, {val})				*test_override()*
 		Overrides certain parts of Vims internal processing to be able
 		to run tests. Only to be used for testing Vim!