add tests for the sub() method and function when the match fails

src/tests/sub.vtc

@@ -2,7 +2,6 @@
 
 varnishtest "sub() method and function"
 
-# Tests from re2 testing/re2_test.cc
 varnish v1 -vcl {
 	import re2 from "${vmod_topbuild}/src/.libs/libvmod_re2.so";
 	backend be { .host = "${bad_ip}"; }
@@ -22,6 +21,7 @@ varnish v1 -vcl {
 	}
 
 	sub vcl_synth {
+		# Tests from re2 testing/re2_test.cc
 		set resp.http.pangram
 		 = piglatin.sub("the quick brown fox jumps over the lazy dogs.",
 		                "\2\1ay");
@@ -50,6 +50,10 @@ varnish v1 -vcl {
 		set resp.http.bplusf = re2.sub("b+", "bbbbbb", "bb");
 		set resp.http.bstar1f = re2.sub("b*", "bbbbbb", "bb");
 		set resp.http.bstar2f = re2.sub("b*", "aaaaa", "bb");
+
+		# Match failure
+		set resp.http.bfail = b.sub("acd", "x", "fallbackb");
+		set resp.http.bfailf = re2.sub("b", "acd", "x", "fallbackf");
 	}
 
 } -start
@@ -78,4 +82,7 @@ client c1 {
 	expect resp.http.bplusf == "bb"
 	expect resp.http.bstar1f == "bb"
 	expect resp.http.bstar2f == "bbaaaaa"
+
+	expect resp.http.bfail == "fallbackb"
+	expect resp.http.bfailf == "fallbackf"
 } -run