Duplicate named capture groups: Syntax tests

Parse-time syntax for RegExp literals is already tested. These two files
test runtime RegExp compilation, with respect to duplicate named capture
groups.

See: tc39#3704

test/annexB/built-ins/RegExp/prototype/compile/duplicate-named-capturing-groups-syntax.js

@@ -0,0 +1,20 @@
+// Copyright 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-regexp.prototype.compile
+description: Runtime parsing of syntax for duplicate named capturing groups
+features: [regexp-duplicate-named-groups]
+---*/
+
+let r = /[ab]/;
+
+assert.throws(
+  SyntaxError,
+  () => r.compile("(?<x>a)(?<x>b)"),
+  "Duplicate named capturing groups in the same alternative do not parse"
+);
+
+let source = "(?<x>a)|(?<x>b)";
+r.compile(source);
+assert.sameValue(r.source, source, "Duplicate named capturing groups in separate alternatives parse correctly");

test/built-ins/RegExp/duplicate-named-capturing-groups-syntax.js

@@ -0,0 +1,18 @@
+// Copyright 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-regexp-pattern-flags
+description: Runtime parsing of syntax for duplicate named capturing groups
+features: [regexp-duplicate-named-groups]
+---*/
+
+assert.throws(
+  SyntaxError,
+  () => new RegExp("(?<x>a)(?<x>b)"),
+  "Duplicate named capturing groups in the same alternative do not parse"
+);
+
+let source = "(?<x>a)|(?<x>b)";
+let parsed = new RegExp(source);
+assert.sameValue(parsed.source, source, "Duplicate named capturing groups in separate alternatives parse correctly");