add test

test/convert-expression/step-values-conversion-test.js

@@ -4,10 +4,16 @@ const { expect } = require('chai');
 var conversion = require('../../src/convert-expression/step-values-conversion');
 
 describe('step-values-conversion.js', () => {
-    it('shuld convert step values', () => {
+    it('should convert step values', () => {
         var expressions = '1,2,3,4,5,6,7,8,9,10/2 0,1,2,3,4,5,6,7,8,9/5 * * * *'.split(' ');
         expressions = conversion(expressions);
         expect(expressions[0]).to.equal('2,4,6,8,10');
         expect(expressions[1]).to.equal('0,5');
     });
+
+    it('should throw an error if step value is not a number', () => {
+        var expressions = '1,2,3,4,5,6,7,8,9,10/someString 0,1,2,3,4,5,6,7,8,9/5 * * * *'.split(' ');
+        expect(() => conversion(expressions)).to.throw('someString is not a valid step value');
+    });
+
 });