Add template literal tests for supplementary-plane unicode escape sequences

test/language/expressions/template-literal/tv-utf16-escape-sequence-supplementary.js

@@ -0,0 +1,95 @@
+// Copyright (C) 2026 hexbinoct. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-static-semantics-tv
+description: >
+    Template values of \u{} escape sequences for code points above U+FFFF
+info: |
+    The TV of TemplateCharacter :: \ TemplateEscapeSequence is the SV of
+    TemplateEscapeSequence.
+    The SV of UnicodeEscapeSequence :: u{ CodePoint } is the result of
+    performing UTF16EncodeCodePoint on the MV of CodePoint.
+
+    UTF16EncodeCodePoint ( cp )
+
+    1. Assert: 0 <= cp <= 0x10FFFF.
+    2. If cp <= 0xFFFF, return the String value consisting of the code unit
+       whose numeric value is cp.
+    3. Let cu1 be the code unit whose numeric value is
+       floor((cp - 0x10000) / 0x400) + 0xD800.
+    4. Let cu2 be the code unit whose numeric value is
+       ((cp - 0x10000) modulo 0x400) + 0xDC00.
+    5. Return the string-concatenation of cu1 and cu2.
+
+    Steps 3 through 5 are reached only for code points in the range 0x10000
+    through 0x10FFFF, which encode as a surrogate pair.
+---*/
+
+var calls;
+
+calls = 0;
+(function(s) {
+  calls++;
+  assert.sameValue(
+    s[0],
+    '\uD800\uDC00',
+    'template value of U+10000, the least code point encoded as a surrogate pair'
+  );
+  assert.sameValue(
+    s.raw[0], '\\u{10000}', 'template raw value of \\u{10000}'
+  );
+})`\u{10000}`;
+assert.sameValue(calls, 1);
+
+calls = 0;
+(function(s) {
+  calls++;
+  assert.sameValue(
+    s[0],
+    '\uD801\uDC37',
+    'template value of U+10437'
+  );
+  assert.sameValue(
+    s.raw[0], '\\u{10437}', 'template raw value of \\u{10437}'
+  );
+})`\u{10437}`;
+assert.sameValue(calls, 1);
+
+calls = 0;
+(function(s) {
+  calls++;
+  assert.sameValue(
+    s[0],
+    '\uDBFF\uDFFF',
+    'template value of U+10FFFF, the greatest code point'
+  );
+  assert.sameValue(
+    s.raw[0], '\\u{10FFFF}', 'template raw value of \\u{10FFFF}'
+  );
+})`\u{10FFFF}`;
+assert.sameValue(calls, 1);
+
+calls = 0;
+(function(s) {
+  calls++;
+  assert.sameValue(
+    s[0],
+    '\uD800\uDC00',
+    'template value of U+10000 (with leading zeros)'
+  );
+  assert.sameValue(
+    s.raw[0], '\\u{010000}', 'template raw value of \\u{010000}'
+  );
+})`\u{010000}`;
+assert.sameValue(calls, 1);
+
+assert.sameValue(
+  `\u{10437}`,
+  '\uD801\uDC37',
+  'template value in an untagged template literal'
+);
+assert.sameValue(
+  `a\u{10437}b`,
+  'a\uD801\uDC37b',
+  'surrogate pair concatenates with adjacent template characters'
+);