diff --git a/tests/es.js b/tests/es.js
index 598ec1d61bd0..43576993923f 100644
--- a/tests/es.js
+++ b/tests/es.js
@@ -2745,33 +2745,33 @@
     assert.name(toPrecision, 'toPrecision');
     assert.arity(toPrecision, 1);
     assert.looksNative(toPrecision);
-    assert.same(0.00008.toPrecision(3), '0.0000800');
-    assert.same(1.255.toPrecision(2), '1.3');
-    assert.same(1843654265.0774949.toPrecision(13), '1843654265.077');
-    assert.same(NaN.toPrecision(1), 'NaN');
-    assert.same(123.456.toPrecision(), '123.456');
-    assert.same(123.456.toPrecision(void 8), '123.456');
+    assert.same(0.00008.toPrecision(3), '0.0000800', '0.00008.toPrecision(3)');
+    assert.same(1.255.toPrecision(2), '1.3', '1.255.toPrecision(2)');
+    assert.same(1843654265.0774949.toPrecision(13), '1843654265.077', '1843654265.0774949.toPrecision(13)');
+    assert.same(NaN.toPrecision(1), 'NaN', 'If x is NaN, return the String "NaN".');
+    assert.same(123.456.toPrecision(), '123.456', 'If precision is undefined, return ! ToString(x).');
+    assert.same(123.456.toPrecision(void 8), '123.456', 'If precision is undefined, return ! ToString(x).');
     assert.throws(function(){
       0.9.toPrecision(0);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
       0.9.toPrecision(101);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
-      return toPrecision.call({}, 1);
-    }, TypeError);
+      toPrecision.call({}, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call('123', 1);
-    }, TypeError);
+      toPrecision.call('123', 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(false, 1);
-    }, TypeError);
+      toPrecision.call(false, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(null, 1);
-    }, TypeError);
+      toPrecision.call(null, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(void 8, 1);
-    }, TypeError);
+      toPrecision.call(void 8, 1);
+    }, TypeError, '? thisNumberValue(this value)');
   });
 }).call(this);
 
diff --git a/tests/library.js b/tests/library.js
index b95dbf880e15..264bb4d47ac2 100644
--- a/tests/library.js
+++ b/tests/library.js
@@ -2801,33 +2801,33 @@
     var toPrecision;
     toPrecision = core.Number.toPrecision;
     assert.isFunction(toPrecision);
-    assert.same(toPrecision(0.00008, 3), '0.0000800');
-    assert.same(toPrecision(1.255, 2), '1.3');
-    assert.same(toPrecision(1843654265.0774949, 13), '1843654265.077');
-    assert.same(toPrecision(NaN, 1), 'NaN');
-    assert.same(toPrecision(123.456), '123.456');
-    assert.same(toPrecision(123.456, void 8), '123.456');
+    assert.same(toPrecision(0.00008, 3), '0.0000800', '0.00008.toPrecision(3)');
+    assert.same(toPrecision(1.255, 2), '1.3', '1.255.toPrecision(2)');
+    assert.same(toPrecision(1843654265.0774949, 13), '1843654265.077', '1843654265.0774949.toPrecision(13)');
+    assert.same(toPrecision(NaN, 1), 'NaN', 'If x is NaN, return the String "NaN".');
+    assert.same(toPrecision(123.456), '123.456', 'If precision is undefined, return ! ToString(x).');
+    assert.same(toPrecision(123.456, void 8), '123.456', 'If precision is undefined, return ! ToString(x).');
     assert.throws(function(){
       toPrecision(0.9, 0);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
       toPrecision(0.9, 101);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
-      return toPrecision({}, 1);
-    }, TypeError);
+      toPrecision({}, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision('123', 1);
-    }, TypeError);
+      toPrecision('123', 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision(false, 1);
-    }, TypeError);
+      toPrecision(false, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision(null, 1);
-    }, TypeError);
+      toPrecision(null, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision(void 8, 1);
-    }, TypeError);
+      toPrecision(void 8, 1);
+    }, TypeError, '? thisNumberValue(this value)');
   });
 }).call(this);
 
diff --git a/tests/library/es6.number.to-precision.ls b/tests/library/es6.number.to-precision.ls
index d63833fabb18..c9ab97072cf3 100644
--- a/tests/library/es6.number.to-precision.ls
+++ b/tests/library/es6.number.to-precision.ls
@@ -4,16 +4,16 @@ module \ES6
 test 'Number#toPrecision' (assert)!->
   {toPrecision} = core.Number
   assert.isFunction toPrecision
-  assert.same toPrecision(0.00008 3), '0.0000800'
-  assert.same toPrecision(1.255 2), '1.3'
-  assert.same toPrecision(1843654265.0774949 13), '1843654265.077'
-  assert.same toPrecision(NaN, 1), 'NaN'
-  assert.same toPrecision(123.456), '123.456'
-  assert.same toPrecision(123.456 void), '123.456'
-  assert.throws (!-> toPrecision 0.9 0), RangeError
-  assert.throws (!-> toPrecision 0.9 101), RangeError
-  assert.throws (-> toPrecision {}, 1), TypeError
-  assert.throws (-> toPrecision \123, 1), TypeError
-  assert.throws (-> toPrecision no, 1), TypeError
-  assert.throws (-> toPrecision null, 1), TypeError
-  assert.throws (-> toPrecision void, 1), TypeError
\ No newline at end of file
+  assert.same toPrecision(0.00008 3), '0.0000800', '0.00008.toPrecision(3)'
+  assert.same toPrecision(1.255 2), '1.3', '1.255.toPrecision(2)'
+  assert.same toPrecision(1843654265.0774949 13), '1843654265.077', '1843654265.0774949.toPrecision(13)'
+  assert.same toPrecision(NaN, 1), 'NaN', 'If x is NaN, return the String "NaN".'
+  assert.same toPrecision(123.456), '123.456', 'If precision is undefined, return ! ToString(x).'
+  assert.same toPrecision(123.456 void), '123.456', 'If precision is undefined, return ! ToString(x).'
+  assert.throws (!-> toPrecision 0.9 0), RangeError, 'If p < 1 or p > 21, throw a RangeError exception.'
+  assert.throws (!-> toPrecision 0.9 101), RangeError, 'If p < 1 or p > 21, throw a RangeError exception.'
+  assert.throws (!-> toPrecision {}, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision \123, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision no, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision null, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision void, 1), TypeError, '? thisNumberValue(this value)'
\ No newline at end of file
diff --git a/tests/tests.js b/tests/tests.js
index f5e0be5829ee..40eed695db62 100644
--- a/tests/tests.js
+++ b/tests/tests.js
@@ -3556,33 +3556,33 @@
     assert.name(toPrecision, 'toPrecision');
     assert.arity(toPrecision, 1);
     assert.looksNative(toPrecision);
-    assert.same(0.00008.toPrecision(3), '0.0000800');
-    assert.same(1.255.toPrecision(2), '1.3');
-    assert.same(1843654265.0774949.toPrecision(13), '1843654265.077');
-    assert.same(NaN.toPrecision(1), 'NaN');
-    assert.same(123.456.toPrecision(), '123.456');
-    assert.same(123.456.toPrecision(void 8), '123.456');
+    assert.same(0.00008.toPrecision(3), '0.0000800', '0.00008.toPrecision(3)');
+    assert.same(1.255.toPrecision(2), '1.3', '1.255.toPrecision(2)');
+    assert.same(1843654265.0774949.toPrecision(13), '1843654265.077', '1843654265.0774949.toPrecision(13)');
+    assert.same(NaN.toPrecision(1), 'NaN', 'If x is NaN, return the String "NaN".');
+    assert.same(123.456.toPrecision(), '123.456', 'If precision is undefined, return ! ToString(x).');
+    assert.same(123.456.toPrecision(void 8), '123.456', 'If precision is undefined, return ! ToString(x).');
     assert.throws(function(){
       0.9.toPrecision(0);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
       0.9.toPrecision(101);
-    }, RangeError);
+    }, RangeError, 'If p < 1 or p > 21, throw a RangeError exception.');
     assert.throws(function(){
-      return toPrecision.call({}, 1);
-    }, TypeError);
+      toPrecision.call({}, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call('123', 1);
-    }, TypeError);
+      toPrecision.call('123', 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(false, 1);
-    }, TypeError);
+      toPrecision.call(false, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(null, 1);
-    }, TypeError);
+      toPrecision.call(null, 1);
+    }, TypeError, '? thisNumberValue(this value)');
     assert.throws(function(){
-      return toPrecision.call(void 8, 1);
-    }, TypeError);
+      toPrecision.call(void 8, 1);
+    }, TypeError, '? thisNumberValue(this value)');
   });
 }).call(this);
 
diff --git a/tests/tests/es6.number.to-precision.ls b/tests/tests/es6.number.to-precision.ls
index 1e13b3da4240..841372546c47 100644
--- a/tests/tests/es6.number.to-precision.ls
+++ b/tests/tests/es6.number.to-precision.ls
@@ -7,16 +7,16 @@ test 'Number#toPrecision' (assert)!->
   assert.name toPrecision, \toPrecision
   assert.arity toPrecision, 1
   assert.looksNative toPrecision
-  assert.same 0.00008.toPrecision(3), '0.0000800'
-  assert.same 1.255.toPrecision(2), '1.3'
-  assert.same 1843654265.0774949.toPrecision(13), '1843654265.077'
-  assert.same NaN.toPrecision(1), 'NaN'
-  assert.same 123.456.toPrecision!, '123.456'
-  assert.same 123.456.toPrecision(void), '123.456'
-  assert.throws (!-> 0.9.toPrecision 0), RangeError
-  assert.throws (!-> 0.9.toPrecision 101), RangeError
-  assert.throws (-> toPrecision.call {}, 1), TypeError
-  assert.throws (-> toPrecision.call \123, 1), TypeError
-  assert.throws (-> toPrecision.call no, 1), TypeError
-  assert.throws (-> toPrecision.call null, 1), TypeError
-  assert.throws (-> toPrecision.call void, 1), TypeError
\ No newline at end of file
+  assert.same 0.00008.toPrecision(3), '0.0000800', '0.00008.toPrecision(3)'
+  assert.same 1.255.toPrecision(2), '1.3', '1.255.toPrecision(2)'
+  assert.same 1843654265.0774949.toPrecision(13), '1843654265.077', '1843654265.0774949.toPrecision(13)'
+  assert.same NaN.toPrecision(1), 'NaN', 'If x is NaN, return the String "NaN".'
+  assert.same 123.456.toPrecision!, '123.456', 'If precision is undefined, return ! ToString(x).'
+  assert.same 123.456.toPrecision(void), '123.456', 'If precision is undefined, return ! ToString(x).'
+  assert.throws (!-> 0.9.toPrecision 0), RangeError, 'If p < 1 or p > 21, throw a RangeError exception.'
+  assert.throws (!-> 0.9.toPrecision 101), RangeError, 'If p < 1 or p > 21, throw a RangeError exception.'
+  assert.throws (!-> toPrecision.call {}, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision.call \123, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision.call no, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision.call null, 1), TypeError, '? thisNumberValue(this value)'
+  assert.throws (!-> toPrecision.call void, 1), TypeError, '? thisNumberValue(this value)'
\ No newline at end of file