Add tests for BigInt.prototype.valueOf (#1234)

* BigInt valueOf tests

* add features from typeCoercion.js

harness/typeCoercion.js

@@ -407,3 +407,19 @@ function testNotCoercibleToBigInt(test) {
   testStringValue("0xg");
   testStringValue("1n");
 }
+
+function testCoercibleToBigIntThisValue(value, test) {
+  test(value);
+  test(Object(value));
+}
+
+function testNotCoercibleToBigIntThisValue(test) {
+  test(undefined);
+  test(null);
+  test(true);
+  test(false);
+  test("");
+  test(Symbol(""));
+  test(0);
+  test({});
+}

test/built-ins/BigInt/prototype/valueOf/length.js

+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.valueof
+description: BigInt.prototype.valueOf.length property descriptor
+info: >
+  BigInt.prototype.valueOf ( )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+verifyProperty(BigInt.prototype.valueOf, "length", {
+  value: 0,
+  writable: false,
+  enumerable: false,
+  configurable: true
+});

test/built-ins/BigInt/prototype/valueOf/name.js

+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.valueof
+description: BigInt.prototype.valueOf.name property descriptor
+info: >
+  BigInt.prototype.valueOf ( )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+verifyProperty(BigInt.prototype.valueOf, "name", {
+  value: "valueOf",
+  writable: false,
+  enumerable: false,
+  configurable: true
+});

test/built-ins/BigInt/prototype/valueOf/prop-desc.js

+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.valueof
+description: BigInt.prototype.valueOf property descriptor
+info: >
+  BigInt.prototype.valueOf ( )
+
+  17 ECMAScript Standard Built-in Objects
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+verifyProperty(BigInt.prototype, "valueOf", {
+  writable: true,
+  enumerable: false,
+  configurable: true
+});

test/built-ins/BigInt/prototype/valueOf/this-value-err.js

+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.valueof
+description: BigInt.prototype.valueOf this value coercion
+info: >
+  BigInt.prototype.valueOf ( )
+
+  Return ? thisBigIntValue(this value).
+includes: [typeCoercion.js]
+features: [BigInt, arrow-function, Symbol, Symbol.toPrimitive]
+---*/
+
+testNotCoercibleToBigIntThisValue(
+  (x) => assert.throws(TypeError, () => BigInt.prototype.valueOf.call(x))
+);

test/built-ins/BigInt/prototype/valueOf/this-value.js

+// Copyright (C) 2017 Robin Templeton. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-bigint.prototype.valueof
+description: BigInt.prototype.valueOf this value coercion
+info: >
+  BigInt.prototype.valueOf ( )
+
+  Return ? thisBigIntValue(this value). 
+includes: [typeCoercion.js]
+features: [BigInt, arrow-function, Symbol, Symbol.toPrimitive]
+---*/
+
+testCoercibleToBigIntThisValue(
+  0n,
+  (x) => assert.sameValue(0n, BigInt.prototype.valueOf.call(x))
+);