Fix typo

doc/Language/testing.pod

@@ -247,7 +247,7 @@ passes the test if the comparison yields a C<True> value. The C<$description>
 of the test is optional.
 
 The C<$comparison> comparator can be either a L<Callable> or 
-a L<Str> containing aninfix operator, such as C<'=='>, a C<'~~'>, or a
+a L<Str> containing an infix operator, such as C<'=='>, a C<'~~'>, or a
 user-defined infix.
 
     cmp-ok 'my spelling is apperling', '~~', /perl/, "bad speller";