diff --git a/harness/typeCoercion.js b/harness/typeCoercion.js
index 296694fcfbf74f05bb8ca891fd153459ab5d9ecf..7cd6a9de3c2bb548b2a2a07f604754770f24bd82 100644
--- a/harness/typeCoercion.js
+++ b/harness/typeCoercion.js
@@ -6,6 +6,20 @@ description: |
     operations like ToNumber.
 ---*/
 
+function testCoercibleToIndexZero(test) {
+  testCoercibleToIntegerZero(test);
+}
+
+function testCoercibleToIndexOne(test) {
+  testCoercibleToIntegerOne(test);
+}
+
+function testCoercibleToIndexFromIndex(nominalIndex, test) {
+  assert(Number.isInteger(nominalIndex));
+  assert(0 <= nominalIndex && nominalIndex <= 2**53 - 1);
+  testCoercibleToIntegerFromInteger(nominalIndex, test);
+}
+
 function testCoercibleToIntegerZero(test) {
   testCoercibleToNumberZero(test);
 
@@ -176,10 +190,35 @@ function testCoercibleToPrimitiveWithMethod(hint, method, test) {
   });
 }
 
+function testNotCoercibleToIndex(test) {
+  function testPrimitiveValue(value) {
+    test(RangeError, value);
+    // ToPrimitive
+    testPrimitiveWrappers(value, "number", function(value) {
+      test(RangeError, value);
+    });
+  }
+
+  // Let integerIndex be ? ToInteger(value).
+  testNotCoercibleToInteger(test);
+
+  // If integerIndex < 0, throw a RangeError exception.
+  testPrimitiveValue(-1);
+  testPrimitiveValue(-2.5);
+  testPrimitiveValue("-2.5");
+  testPrimitiveValue(-Infinity);
+
+  // Let index be ! ToLength(integerIndex).
+  // If SameValueZero(integerIndex, index) is false, throw a RangeError exception.
+  testPrimitiveValue(2 ** 53);
+  testPrimitiveValue(Infinity);
+}
+
 function testNotCoercibleToInteger(test) {
   // ToInteger only throws from ToNumber.
-  return testNotCoercibleToNumber(test);
+  testNotCoercibleToNumber(test);
 }
+
 function testNotCoercibleToNumber(test) {
   function testPrimitiveValue(value) {
     test(TypeError, value);
@@ -283,3 +322,88 @@ function testNotCoercibleToString(test) {
   // ToPrimitive
   testNotCoercibleToPrimitive("string", test);
 }
+
+function testCoercibleToBigIntZero(test) {
+  function testPrimitiveValue(value) {
+    test(value);
+    // ToPrimitive
+    testPrimitiveWrappers(value, "number", test);
+  }
+
+  testCoercibleToBigIntFromBigInt(0n, test);
+  testPrimitiveValue(-0n);
+  testPrimitiveValue("-0");
+  testPrimitiveValue(false);
+  testPrimitiveValue("");
+  testPrimitiveValue("   ");
+
+  // toString() returns ""
+  test([]);
+
+  // toString() returns "0"
+  test([0]);
+}
+
+function testCoercibleToBigIntOne(test) {
+  function testPrimitiveValue(value) {
+    test(value);
+    // ToPrimitive
+    testPrimitiveWrappers(value, "number", test);
+  }
+
+  testCoercibleToBigIntFromBigInt(1n, test);
+  testPrimitiveValue(true);
+
+  // toString() returns "1"
+  test([1]);
+}
+
+function testCoercibleToBigIntFromBigInt(nominalBigInt, test) {
+  function testPrimitiveValue(value) {
+    test(value);
+    // ToPrimitive
+    testPrimitiveWrappers(value, "number", test);
+  }
+
+  testPrimitiveValue(nominalBigInt);
+  testPrimitiveValue(nominalBigInt.toString());
+  testPrimitiveValue("0b" + nominalBigInt.toString(2));
+  testPrimitiveValue("0o" + nominalBigInt.toString(8));
+  testPrimitiveValue("0x" + nominalBigInt.toString(16));
+  testPrimitiveValue("   " + nominalBigInt.toString() + "   ");
+
+  // toString() returns the decimal string representation
+  test([nominalBigInt]);
+  test([nominalBigInt.toString()]);
+}
+
+function testNotCoercibleToBigInt(test) {
+  function testPrimitiveValue(error, value) {
+    test(error, value);
+    // ToPrimitive
+    testPrimitiveWrappers(value, "number", function(value) {
+      test(error, value);
+    });
+  }
+
+  // Undefined, Null, Number, Symbol -> TypeError
+  testPrimitiveValue(TypeError, undefined);
+  testPrimitiveValue(TypeError, null);
+  testPrimitiveValue(TypeError, 0);
+  testPrimitiveValue(TypeError, NaN);
+  testPrimitiveValue(TypeError, Infinity);
+  testPrimitiveValue(TypeError, Symbol("1"));
+
+  // when a String parses to NaN -> SyntaxError
+  function testStringValue(string) {
+    testPrimitiveValue(SyntaxError, string);
+    testPrimitiveValue(SyntaxError, "   " + string);
+    testPrimitiveValue(SyntaxError, string + "   ");
+    testPrimitiveValue(SyntaxError, "   " + string + "   ");
+  }
+  testStringValue("a");
+  testStringValue("0b2");
+  testStringValue("0o8");
+  testStringValue("0xg");
+  testStringValue("1n");
+}
diff --git a/test/built-ins/BigInt/asIntN/bigint-tobigint.js b/test/built-ins/BigInt/asIntN/bigint-tobigint.js
index 44a919c7a45abfbff9009e1188e6f7797a8b9c69..568f00c503aae712e470b8dd704246476ae5bfe9 100644
--- a/test/built-ins/BigInt/asIntN/bigint-tobigint.js
+++ b/test/built-ins/BigInt/asIntN/bigint-tobigint.js
@@ -8,24 +8,26 @@ info: >
 
   2. Let bigint ? ToBigInt(bigint).
 
-features: [BigInt, Symbol, Symbol.toPrimitive, arrow-function]
+features: [BigInt, Symbol, Symbol.toPrimitive]
+includes: [typeCoercion.js]
 ---*/
 
-function MyError() {}
+testCoercibleToBigIntZero(function(zero) {
+  assert.sameValue(BigInt.asIntN(2, zero), 0n);
+});
 
-assert.sameValue(BigInt.asIntN(3, Object(10n)), 2n);
-assert.sameValue(BigInt.asIntN(3, {[Symbol.toPrimitive]:()=>10n, valueOf(){throw new MyError();}, toString(){throw new MyError();}}), 2n);
-assert.sameValue(BigInt.asIntN(3, {valueOf:()=>10n, toString(){throw new MyError();}}), 2n);
-assert.sameValue(BigInt.asIntN(3, {toString:()=>"10"}), 2n);
-assert.throws(MyError, () => BigInt.asIntN(0, {[Symbol.toPrimitive](){throw new MyError();}, valueOf:()=>10n, toString:()=>"10"}));
-assert.throws(MyError, () => BigInt.asIntN(0, {valueOf(){throw new MyError();}, toString:()=>"10"}));
-assert.throws(MyError, () => BigInt.asIntN(0, {toString(){throw new MyError();}}));
-assert.throws(TypeError, () => BigInt.asIntN(0, undefined));
-assert.throws(TypeError, () => BigInt.asIntN(0, null));
-assert.sameValue(BigInt.asIntN(2, true), 1n);
-assert.sameValue(BigInt.asIntN(2, false), 0n);
-assert.throws(TypeError, () => BigInt.asIntN(0, 0));
-assert.throws(SyntaxError, () => BigInt.asIntN(0, "foo"));
-assert.sameValue(BigInt.asIntN(3, "10"), 2n);
-assert.sameValue(BigInt.asIntN(4, "12345678901234567890003"), 3n);
-assert.throws(TypeError, () => BigInt.asIntN(0, Symbol("1")));
+testCoercibleToBigIntOne(function(one) {
+  assert.sameValue(BigInt.asIntN(2, one), 1n);
+});
+
+testCoercibleToBigIntFromBigInt(10n, function(ten) {
+  assert.sameValue(BigInt.asIntN(3, ten), 2n);
+});
+
+testCoercibleToBigIntFromBigInt(12345678901234567890003n, function(value) {
+  assert.sameValue(BigInt.asIntN(4, value), 3n);
+});
+
+testNotCoercibleToBigInt(function(error, value) {
+  assert.throws(error, function() { BigInt.asIntN(0, value); });
+});
diff --git a/test/built-ins/BigInt/asIntN/bits-toindex.js b/test/built-ins/BigInt/asIntN/bits-toindex.js
index 76a61564d4c3b39131cb64de02322a98d02a5981..137fc78806ccae2d787bfe75e26827513808a392 100644
--- a/test/built-ins/BigInt/asIntN/bits-toindex.js
+++ b/test/built-ins/BigInt/asIntN/bits-toindex.js
@@ -8,30 +8,22 @@ info: >
 
   1. Let bits be ? ToIndex(bits).
 
-features: [BigInt, Symbol, Symbol.toPrimitive, arrow-function]
+features: [BigInt, Symbol, Symbol.toPrimitive]
+includes: [typeCoercion.js]
 ---*/
 
-function MyError() {}
+testCoercibleToIndexZero(function(zero) {
+  assert.sameValue(BigInt.asIntN(zero, 1n), 0n);
+});
 
-assert.sameValue(BigInt.asIntN(undefined, 1n), 0n);
-assert.sameValue(BigInt.asIntN(null, 1n), 0n);
-assert.sameValue(BigInt.asIntN(true, 1n), -1n);
-assert.sameValue(BigInt.asIntN(false, 1n), 0n);
-assert.sameValue(BigInt.asIntN("foo", 1n), 0n);
-assert.sameValue(BigInt.asIntN("3", 10n), 2n);
-assert.throws(TypeError, () => BigInt.asIntN(Symbol(0), 0n));
-assert.throws(TypeError, () => BigInt.asIntN(1n, 0n));
-assert.sameValue(BigInt.asIntN(Object(3), 10n), 2n);
-assert.sameValue(BigInt.asIntN({[Symbol.toPrimitive]:()=>3, valueOf(){throw new MyError();}, toString(){throw new MyError();}}, 10n), 2n);
-assert.sameValue(BigInt.asIntN({valueOf:()=>3, toString(){throw new MyError();}}, 10n), 2n);
-assert.sameValue(BigInt.asIntN({toString:()=>"3"}, 10n), 2n);
-assert.throws(MyError, () => BigInt.asIntN({[Symbol.toPrimitive](){throw new MyError();}, valueOf:()=>3, toString:()=>"3"}, 0n));
-assert.throws(MyError, () => BigInt.asIntN({valueOf(){throw new MyError();}, toString:()=>"3"}, 0n));
-assert.throws(MyError, () => BigInt.asIntN({toString(){throw new MyError();}}, 0n));
-assert.sameValue(BigInt.asIntN(NaN, 1n), 0n);
-assert.sameValue(BigInt.asIntN(3.9, 10n), 2n);
-assert.sameValue(BigInt.asIntN(-0.9, 1n), 0n);
-assert.throws(RangeError, () => BigInt.asIntN(-1, 0n));
-assert.throws(RangeError, () => BigInt.asIntN("-2.5", 0n));
-assert.throws(RangeError, () => BigInt.asIntN(2 ** 53, 0n));
-assert.throws(RangeError, () => BigInt.asIntN(Infinity, 0n));
+testCoercibleToIndexOne(function(one) {
+  assert.sameValue(BigInt.asIntN(one, 1n), -1n);
+});
+
+testCoercibleToIndexFromIndex(3, function(three) {
+  assert.sameValue(BigInt.asIntN(three, 10n), 2n);
+});
+
+testNotCoercibleToIndex(function(error, value) {
+  assert.throws(error, function() { BigInt.asIntN(value, 0n); });
+});
diff --git a/test/built-ins/BigInt/asUintN/arithmetic.js b/test/built-ins/BigInt/asUintN/arithmetic.js
new file mode 100644
index 0000000000000000000000000000000000000000..abdf9df81f25be8e4c77f1f78a90fe4cfed56130
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/arithmetic.js
@@ -0,0 +1,69 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN arithmetic test cases
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  3. Return a BigInt representing bigint modulo 2**bits.
+
+features: [BigInt]
+---*/
+
+assert.sameValue(BigInt.asUintN(0, -2n), 0n);
+assert.sameValue(BigInt.asUintN(0, -1n), 0n);
+assert.sameValue(BigInt.asUintN(0,  0n), 0n);
+assert.sameValue(BigInt.asUintN(0,  1n), 0n);
+assert.sameValue(BigInt.asUintN(0,  2n), 0n);
+
+assert.sameValue(BigInt.asUintN(1, -3n), 1n);
+assert.sameValue(BigInt.asUintN(1, -2n), 0n);
+assert.sameValue(BigInt.asUintN(1, -1n), 1n);
+assert.sameValue(BigInt.asUintN(1,  0n), 0n);
+assert.sameValue(BigInt.asUintN(1,  1n), 1n);
+assert.sameValue(BigInt.asUintN(1,  2n), 0n);
+assert.sameValue(BigInt.asUintN(1,  3n), 1n);
+assert.sameValue(BigInt.asUintN(1, -123456789012345678901n), 1n);
+assert.sameValue(BigInt.asUintN(1, -123456789012345678900n), 0n);
+assert.sameValue(BigInt.asUintN(1,  123456789012345678900n), 0n);
+assert.sameValue(BigInt.asUintN(1,  123456789012345678901n), 1n);
+
+assert.sameValue(BigInt.asUintN(2, -3n), 1n);
+assert.sameValue(BigInt.asUintN(2, -2n), 2n);
+assert.sameValue(BigInt.asUintN(2, -1n), 3n);
+assert.sameValue(BigInt.asUintN(2,  0n), 0n);
+assert.sameValue(BigInt.asUintN(2,  1n), 1n);
+assert.sameValue(BigInt.asUintN(2,  2n), 2n);
+assert.sameValue(BigInt.asUintN(2,  3n), 3n);
+assert.sameValue(BigInt.asUintN(2, -123456789012345678901n), 3n);
+assert.sameValue(BigInt.asUintN(2, -123456789012345678900n), 0n);
+assert.sameValue(BigInt.asUintN(2,  123456789012345678900n), 0n);
+assert.sameValue(BigInt.asUintN(2,  123456789012345678901n), 1n);
+
+assert.sameValue(BigInt.asUintN(8, 0xabn), 0xabn);
+assert.sameValue(BigInt.asUintN(8, 0xabcdn), 0xcdn);
+assert.sameValue(BigInt.asUintN(8, 0xabcdef01n), 0x01n);
+assert.sameValue(BigInt.asUintN(8, 0xabcdef0123456789abcdef0123n), 0x23n);
+assert.sameValue(BigInt.asUintN(8, 0xabcdef0123456789abcdef0183n), 0x83n);
+
+assert.sameValue(BigInt.asUintN(64, 0xabcdef0123456789abcdefn),  0x0123456789abcdefn);
+assert.sameValue(BigInt.asUintN(65, 0xabcdef0123456789abcdefn), 0x10123456789abcdefn);
+
+assert.sameValue(BigInt.asUintN(200,
+  0xbffffffffffffffffffffffffffffffffffffffffffffffffffn),
+  0x0ffffffffffffffffffffffffffffffffffffffffffffffffffn
+);
+assert.sameValue(BigInt.asUintN(201,
+  0xbffffffffffffffffffffffffffffffffffffffffffffffffffn),
+  0x1ffffffffffffffffffffffffffffffffffffffffffffffffffn
+);
+
+assert.sameValue(BigInt.asUintN(200,
+  0xb89e081df68b65fedb32cffea660e55df9605650a603ad5fc54n),
+  0x089e081df68b65fedb32cffea660e55df9605650a603ad5fc54n
+);
+assert.sameValue(BigInt.asUintN(201,
+  0xb89e081df68b65fedb32cffea660e55df9605650a603ad5fc54n),
+  0x189e081df68b65fedb32cffea660e55df9605650a603ad5fc54n
+);
diff --git a/test/built-ins/BigInt/asUintN/asUintN.js b/test/built-ins/BigInt/asUintN/asUintN.js
new file mode 100644
index 0000000000000000000000000000000000000000..7511687c9b73f904a9cb413f564e0d1e1e2089c2
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/asUintN.js
@@ -0,0 +1,21 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN property descriptor
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  17 ECMAScript Standard Built-in Objects
+
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+assert.sameValue(typeof BigInt.asUintN, 'function');
+
+verifyProperty(BigInt, "asUintN", {
+  enumerable: false,
+  writable: true,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/asUintN/bigint-tobigint.js b/test/built-ins/BigInt/asUintN/bigint-tobigint.js
new file mode 100644
index 0000000000000000000000000000000000000000..2c6229dd1086d5acff1aecbf2f6489ac6525d80a
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/bigint-tobigint.js
@@ -0,0 +1,33 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN type coercion for bigint parameter
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  2. Let bigint ? ToBigInt(bigint).
+
+features: [BigInt, Symbol, Symbol.toPrimitive]
+includes: [typeCoercion.js]
+---*/
+
+testCoercibleToBigIntZero(function(zero) {
+  assert.sameValue(BigInt.asUintN(2, zero), 0n);
+});
+
+testCoercibleToBigIntOne(function(one) {
+  assert.sameValue(BigInt.asUintN(2, one), 1n);
+});
+
+testCoercibleToBigIntFromBigInt(10n, function(ten) {
+  assert.sameValue(BigInt.asUintN(3, ten), 2n);
+});
+
+testCoercibleToBigIntFromBigInt(12345678901234567890003n, function(value) {
+  assert.sameValue(BigInt.asUintN(4, value), 3n);
+});
+
+testNotCoercibleToBigInt(function(error, value) {
+  assert.throws(error, function() { BigInt.asUintN(0, value); });
+});
diff --git a/test/built-ins/BigInt/asUintN/bits-toindex.js b/test/built-ins/BigInt/asUintN/bits-toindex.js
new file mode 100644
index 0000000000000000000000000000000000000000..0d999c242e84412cf4025ef9bb76f0eba0080606
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/bits-toindex.js
@@ -0,0 +1,29 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN type coercion for bits parameter
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  1. Let bits be ? ToIndex(bits).
+
+features: [BigInt, Symbol, Symbol.toPrimitive]
+includes: [typeCoercion.js]
+---*/
+
+testCoercibleToIndexZero(function(zero) {
+  assert.sameValue(BigInt.asUintN(zero, 1n), 0n);
+});
+
+testCoercibleToIndexOne(function(one) {
+  assert.sameValue(BigInt.asUintN(one, 1n), 1n);
+});
+
+testCoercibleToIndexFromIndex(3, function(three) {
+  assert.sameValue(BigInt.asUintN(three, 10n), 2n);
+});
+
+testNotCoercibleToIndex(function(error, value) {
+  assert.throws(error, function() { BigInt.asUintN(value, 0n); });
+});
diff --git a/test/built-ins/BigInt/asUintN/length.js b/test/built-ins/BigInt/asUintN/length.js
new file mode 100644
index 0000000000000000000000000000000000000000..93659f87a662dab866cae98cf467952627dcf47a
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/length.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN.length descriptor
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  17 ECMAScript Standard Built-in Objects
+
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+verifyProperty(BigInt.asUintN, "length", {
+  value: 2,
+  enumerable: false,
+  writable: false,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/asUintN/name.js b/test/built-ins/BigInt/asUintN/name.js
new file mode 100644
index 0000000000000000000000000000000000000000..fc2efebad8e01f4687ce4a89efdc51f82005d427
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/name.js
@@ -0,0 +1,20 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN.name descriptor
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  17 ECMAScript Standard Built-in Objects
+
+includes: [propertyHelper.js]
+features: [BigInt]
+---*/
+
+verifyProperty(BigInt.asUintN, "name", {
+  value: "asUintN",
+  enumerable: false,
+  writable: false,
+  configurable: true
+});
diff --git a/test/built-ins/BigInt/asUintN/order-of-steps.js b/test/built-ins/BigInt/asUintN/order-of-steps.js
new file mode 100644
index 0000000000000000000000000000000000000000..8bfeaef42c9b3ee461b3c121997a76c1a25a241b
--- /dev/null
+++ b/test/built-ins/BigInt/asUintN/order-of-steps.js
@@ -0,0 +1,32 @@
+// Copyright (C) 2017 Josh Wolfe. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: pending
+description: BigInt.asUintN order of parameter type coercion
+info: >
+  BigInt.asUintN ( bits, bigint )
+
+  1. Let bits be ? ToIndex(bits).
+  2. Let bigint ? ToBigInt(bigint).
+
+features: [BigInt]
+---*/
+
+var i = 0;
+var bits = {
+  valueOf() {
+    assert.sameValue(i, 0);
+    i++;
+    return 0;
+  }
+};
+var bigint = {
+  valueOf() {
+    assert.sameValue(i, 1);
+    i++;
+    return 0n;
+  }
+};
+
+BigInt.asUintN(bits, bigint);
+assert.sameValue(i, 2);