add tests for "only coerce once in BigInt constructor"

test/built-ins/BigInt/constructor-coercion.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2022 Kevin Gibbons. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: BigInt constructor only coerces its input once
+esid: sec-bigint-constructor-number-value
+info: |
+  BigInt ( value )
+    1. If NewTarget is not undefined, throw a TypeError exception.
+    2. Let prim be ? ToPrimitive(value, number).
+    3. If Type(prim) is Number, return ? NumberToBigInt(prim).
+    4. Otherwise, return ? ToBigInt(prim).
+features: [BigInt]
+---*/
+
+var first = true;
+var v = {
+  [Symbol.toPrimitive]: function() {
+    if (first) {
+      first = false;
+      return "42";
+    }
+    throw new Test262Error("Symbol.toPrimitive should only be invoked once");
+  },
+};
+
+assert.sameValue(BigInt(v), 42n, "BigInt constructor should use the post-ToPrimitive value as the argument to ToBigInt");