test: refactor test-http-response-splitting

* move repeated code to function
* remove unneeded `common.mustCall()` usage with function arguments that
  are not callbacks
* add error message checking

PR-URL: https://github.com/nodejs/node/pull/11429
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

test/parallel/test-http-response-splitting.js

@@ -19,23 +19,23 @@ const y = 'foo⠊Set-Cookie: foo=bar';
 
 let count = 0;
 
+function test(res, code, header) {
+  assert.throws(() => {
+    res.writeHead(code, header);
+  }, /^TypeError: The header content contains invalid characters$/);
+}
+
 const server = http.createServer((req, res) => {
   switch (count++) {
     case 0:
       const loc = url.parse(req.url, true).query.lang;
-      assert.throws(common.mustCall(() => {
+      test(res, 302, {Location: `/foo?lang=${loc}`});
-        res.writeHead(302, {Location: `/foo?lang=${loc}`});
-      }));
       break;
     case 1:
-      assert.throws(common.mustCall(() => {
+      test(res, 200, {'foo': x});
-        res.writeHead(200, {'foo': x});
-      }));
       break;
     case 2:
-      assert.throws(common.mustCall(() => {
+      test(res, 200, {'foo': y});
-        res.writeHead(200, {'foo': y});
-      }));
       break;
     default:
       common.fail('should not get to here.');