Fix 1190 pattern not return consistent output

src/structs/refinements.ts

@@ -95,8 +95,9 @@ export function pattern<T extends string, S extends any>(
   regexp: RegExp
 ): Struct<T, S> {
   return refine(struct, 'pattern', (value) => {
+    const regexpCopy = new RegExp(regexp) // necessary because of https://stackoverflow.com/questions/3891641/regex-test-only-works-every-other-time
     return (
-      regexp.test(value) ||
+      regexpCopy.test(value) ||
       `Expected a ${struct.type} matching \`/${regexp.source}/\` but received "${value}"`
     )
   })

test/pattern.test.ts

@@ -0,0 +1,16 @@
+import { object, pattern, string, is } from '../src'
+import { describe, expect, it } from 'vitest'
+
+describe('pattern', () => {
+  it('runs pattern twice', () => {
+    const Query = object({
+      url: pattern(string(), /^example/g),
+    })
+
+    const testQuery = {
+      url: 'example',
+    }
+
+    expect(is(testQuery, Query)).toEqual(is(testQuery, Query))
+  })
+})