test: replace assertion error check with regex

PR-URL: #12603
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

Author: TheLady

test/parallel/test-v8-flag-type-check.js

@@ -3,5 +3,7 @@ require('../common');
 const assert = require('assert');
 const v8 = require('v8');
 
-assert.throws(function() { v8.setFlagsFromString(1); }, TypeError);
-assert.throws(function() { v8.setFlagsFromString(); }, TypeError);
+assert.throws(function() { v8.setFlagsFromString(1); },
+              /^TypeError: v8 flag must be a string$/);
+assert.throws(function() { v8.setFlagsFromString(); },
+              /^TypeError: v8 flag is required$/);

test/parallel/test-v8-flags.js

@@ -12,5 +12,7 @@ assert(eval('%_IsSmi(42)'));
 assert(vm.runInThisContext('%_IsSmi(43)'));
 
 v8.setFlagsFromString('--noallow_natives_syntax');
-assert.throws(function() { eval('%_IsSmi(44)'); }, SyntaxError);
-assert.throws(function() { vm.runInThisContext('%_IsSmi(45)'); }, SyntaxError);
+assert.throws(function() { eval('%_IsSmi(44)'); },
+              /^SyntaxError: Unexpected token %$/);
+assert.throws(function() { vm.runInThisContext('%_IsSmi(45)'); },
+              /^SyntaxError: Unexpected token %$/);