Test key not found for a decryption VFP.

src/tests/decrypt.vtc

@@ -347,3 +347,39 @@ client c1 {
 logexpect l1 -wait
 
 varnish v1 -expect ECE.vfp.ece_decrypt.ops == 11
+
+server s1 -wait
+server s1 -start
+
+# Delete the key, so as to provoke a key not found error.
+varnish v1 -vcl+backend {
+	import ${vmod_ece};
+	import blob;
+
+	sub vcl_init {
+		ece.delete_key("");
+	}
+
+	sub vcl_backend_response {
+		set beresp.filters = "ece_decrypt";
+		set beresp.uncacheable = true;
+		set beresp.do_stream = false;
+	}
+}
+
+logexpect l1 -v v1 -d 0 -g vxid -q "FetchError" {
+	expect 0 * Begin	bereq
+	expect * = FetchError	{^ece decrypt failure: unknown key $}
+	expect * = End
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 503
+	expect resp.reason == "Backend fetch failed"
+} -run
+
+logexpect l1 -wait
+
+varnish v1 -expect ECE.vfp.ece_decrypt.ops == 12