Add assert.ifError

doc/api.markdown

@@ -2546,6 +2546,9 @@ Expects `block` to throw an error.
 
 Expects `block` not to throw an error.
 
+### assert.ifError(value)
+
+Tests if value is not a false value, throws if it is a true value. Useful when testing the first argument, `error` in callbacks.
 
 ## Path
 

lib/assert.js

@@ -284,3 +284,4 @@ assert.doesNotThrow = function(block, /*optional*/error, /*optional*/message) {
   _throws.apply(this, [false].concat(pSlice.call(arguments)));
 };
 
+assert.ifError = function (err) { if (err) {throw err;}};

test/simple/test-assert.js

@@ -154,3 +154,6 @@ try {
 }
 assert.equal(true,threw,'a.doesNotThrow is not catching type matching errors');
 
+assert.throws(function () {assert.ifError(new Error('test error'))});
+assert.doesNotThrow(function(){assert.ifError(null)});
+assert.doesNotThrow(function(){assert.ifError()});