It tests combine two strings JS solution.

tests/javascript/combine-two-strings.js

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+var expect = require('chai').expect;
+var combineTwoStrings = require('../../solutions/javascript/combine-two-strings');
+
+describe('it tests combine two strings function', function(){
+  var str1 = 'abc';
+  var str2 = 'def';
+  var str3valid = 'dabecf';
+  var str3invalid = 'dabfce';
+
+  it("it tests that f('" + str1 + "," +str2 + ",'" +str3valid + "')' is valid " , function(){
+    var result = combineTwoStrings(str1, str2, str3valid);
+    expect(result).to.be.true;
+  });
+
+  it("it tests that f('" + str1 + "," +str2 + ",'" +str3invalid + "')' is invalid " , function(){
+    var result = combineTwoStrings(str1, str2, str3invalid);
+    expect(result).to.be.false;
+  });
+
+});