add tests, allow hex function to accept calculator argument

.gitignore

@@ -0,0 +1 @@
+node_modules/

README.md

@@ -67,6 +67,13 @@ batch.srm('mosher');
 // defaults to 'morey'
 batch.ebc();
 // => 28.9000740481361
+
+batch.hex('daniels');
+// => '#B26033'
+
+// defaults to 'morey'
+batch.hex();
+// => '#A85C37'
 ```
 
 ### Options
@@ -82,7 +89,7 @@ Any one of the following options must be passed to the module:
 | `l` or `lovibond` | the degrees Lovibond of a batch | `Number` |
 | `batch` | options describing a batch in detail **(see below)** | `Object` |
 
-This option may be used in combination with the TODO option to specify which calculation method was used:
+This option may be used in combination with a known color value (`srm`, `ebc`, or `l`) to specify which calculation method was used:
 
 | option | description | type |
 |-|-|-|

index.js

@@ -60,23 +60,23 @@ Batch.prototype.l = Batch.prototype.lovibond = function (calculator) {
   return (this.srm(calculator) + 0.6) / 1.35;
 };
 
-Batch.prototype.hex = function () {
-  let deciSRM = Math.max(0, Math.round(this.srm() * 10));
+Batch.prototype.hex = function (calculator) {
+  let deciSRM = Math.max(0, Math.round(this.srm(calculator) * 10));
   return DECI_SRM[Math.min(DECI_SRM.length - 1, deciSRM)];
 };
 
-Batch.srm = {
-  morey:   (mcu) => 1.4922 * Math.pow(mcu, 0.6859),
-  daniels: (mcu) => 0.2 * mcu + 8.4,
-  mosher:  (mcu) => 0.3 * mcu + 4.7,
-  barry:   (mcu) => 1.5 * Math.pow(mcu, 0.7),
-};
-
 Batch.mcu = {
   morey:   (srm) => Math.pow(srm / 1.4922, 1 / 0.6859),
   daniels: (srm) => Math.max(0, srm - 8.4) / 0.2,
   mosher:  (srm) => Math.max(0, srm - 4.7) / 0.3,
   barry:   (srm) => Math.pow(srm / 1.5, 1 / 0.7),
 };
 
+Batch.srm = {
+  morey:   (mcu) => 1.4922 * Math.pow(mcu, 0.6859),
+  daniels: (mcu) => 0.2 * mcu + 8.4,
+  mosher:  (mcu) => 0.3 * mcu + 4.7,
+  barry:   (mcu) => 1.5 * Math.pow(mcu, 0.7),
+};
+
 module.exports = chromabrew;