explicitly allow a delta of 0

Author: koddsson

lib/chai/core/assertions.js

@@ -3027,10 +3027,10 @@ function closeTo(expected, delta, msg) {
 
   new Assertion(obj, flagMsg, ssfi, true).is.numeric;
   let message =  'A `delta` value is required for `closeTo`';
-  if (!delta) throw new AssertionError(flagMsg ? `${flagMsg}: ${message}` : message, undefined, ssfi);
+  if (delta == undefined) throw new AssertionError(flagMsg ? `${flagMsg}: ${message}` : message, undefined, ssfi);
   new Assertion(delta, flagMsg, ssfi, true).is.numeric;
   message =  'A `expected` value is required for `closeTo`';
-  if (!delta) throw new AssertionError(flagMsg ? `${flagMsg}: ${message}` : message, undefined, ssfi);
+  if (expected == undefined) throw new AssertionError(flagMsg ? `${flagMsg}: ${message}` : message, undefined, ssfi);
   new Assertion(expected, flagMsg, ssfi, true).is.numeric;
 
   const abs = (x) => x < 0n ? -x : x;

test/assert.js

@@ -1893,6 +1893,7 @@ describe('assert', function () {
     assert.closeTo(1.5, 1.0, 0.5);
     assert.closeTo(10, 20, 20);
     assert.closeTo(-10, 20, 30);
+    assert.closeTo(10, 10, 0);
 
     err(function(){
       assert.closeTo(2, 1.0, 0.5, 'blah');