diff --git a/package.json b/package.json
index 8d3185e..4c25766 100644
--- a/package.json
+++ b/package.json
@@ -6,8 +6,9 @@
   "scripts": {
     "compile": "babel --presets es2015,stage-0 -d lib/ src/",
     "prepublish": "npm run compile",
-    "test": "node_modules/.bin/_mocha test",
-    "test2": "node_modules/.bin/babel-node node_modules/.bin/babel-istanbul cover node_modules/.bin/_mocha -- test/*.js",
+    "pretest": "npm run compile",
+    "test2": "node_modules/.bin/_mocha test",
+    "test": "node_modules/.bin/babel-node node_modules/.bin/babel-istanbul cover node_modules/.bin/_mocha -- test/*.js",
     "coverage": "istanbul cover _mocha -- --ui bdd -R spec -t 5000;open ./coverage/lcov-report/index.html",
     "cover": "node_modules/.bin/babel-node node_modules/.bin/babel-istanbul cover node_modules/.bin/_mocha",
     "coveralls": "npm run cover -- --report lcovonly && cat ./coverage/lcov.info | coveralls"
@@ -38,14 +39,18 @@
   "devDependencies": {
     "babel-cli": "^6.18.0",
     "babel-core": "^6.18.2",
+    "babel-istanbul": "^0.11.0",
     "babel-polyfill": "^6.16.0",
     "babel-preset-es2015": "^6.18.0",
     "babel-preset-react": "^6.16.0",
     "babel-preset-stage-0": "^6.16.0",
     "coveralls": "^2.11.15",
     "enzyme": "^2.6.0",
+    "expect": "^1.20.2",
+    "mocha": "^3.2.0",
     "mocha-lcov-reporter": "^1.2.0",
-    "react": "^15.4.1"
+    "react": "^15.4.1",
+    "sinon": "^1.17.6"
   },
   "dependencies": {
     "x-object": "^1.0.10"
diff --git a/src/core.js b/src/core.js
index 77f6c8e..f880beb 100644
--- a/src/core.js
+++ b/src/core.js
@@ -13,7 +13,7 @@ export const jsonsHeaders = ((array) => Array.from(
 
 export const jsons2arrays = (jsons, headers) => {
  headers = headers || jsonsHeaders(jsons);
- return [headers, ...array.map((object) =>
+ return [headers, ...jsons.map((object) =>
   headers.map((header) =>
    object[header] ? object[header] : ''))]
 };
diff --git a/test/coreSpec.js b/test/coreSpec.js
new file mode 100644
index 0000000..fc04c63
--- /dev/null
+++ b/test/coreSpec.js
@@ -0,0 +1,181 @@
+import expect from 'expect';
+
+import {
+ isJsons,
+ isArrays,
+ jsonsHeaders,
+ jsons2arrays,
+ arrays2csv,
+ jsons2csv,
+ string2csv,
+ toCSV,
+ buildURI
+} from '../lib/core';
+
+describe(`core::isJsons`, () => {
+ it(`returns true if all items of array are literal objects`, () => {
+  const target = [{}, {}, {}, {}];
+  expect(isJsons(target)).toBeTruthy();
+ });
+ it(`returns false if one of array items is not literal object`, () => {
+  let target = ["", {}, {}, {}];
+  expect(isJsons(target)).toBeFalsy();
+  target = [{},
+   [], {}, {}
+  ];
+  expect(isJsons(target)).toBeFalsy();
+ });
+
+});
+
+describe(`core::isArrays`, () => {
+ it(`retruns true if all array items are arrays too`, () => {
+  const target = [
+   [],
+   [],
+   [],
+   []
+  ];
+  expect(isArrays(target)).toBeTruthy();
+ });
+ it(`retruns false if one of array items is not array`, () => {
+  let target = [{},
+   [],
+   [],
+   []
+  ];
+  expect(isArrays(target)).toBeFalsy();
+  target = [
+   [], new Set([]), [],
+   []
+  ];
+  expect(isArrays(target)).toBeFalsy();
+  target = [
+   [], '[]', [],
+   []
+  ];
+  expect(isArrays(target)).toBeFalsy();
+ });
+
+});
+
+
+describe(`core::jsonsHeaders`, () => {
+ let fixtures;
+ beforeEach(() => {
+  fixtures = [{
+   maths: 90,
+   phy: 80
+  }, {
+   maths: 50,
+   sport: 97,
+   ch: 66
+  }, {
+   ch: 77,
+   sport: 99
+  }]
+ });
+
+ it(`returns union of keys of all array items `, () => {
+   let actual = jsonsHeaders(fixtures);
+   expect(actual).toEqual([`maths`, `phy`, 'sport', 'ch'])
+  }),
+
+  it(`does not duplicate keys on the array`, () => {
+   let actual = jsonsHeaders(fixtures);
+   let keysOfAllItems = fixtures.map((object) => Object.keys(object))
+    .reduce((a, b) => [...a, ...b], []);
+   expect(actual.length).toBeLessThanOrEqualTo(keysOfAllItems.length);
+   expect(actual.length).toEqual(new Set(keysOfAllItems).size);
+
+  })
+
+});
+describe(`core::jsons2arrays`, () => {
+ let fixtures;
+ beforeEach(() => {
+  fixtures = [{
+   maths: '90'
+  }, {
+   sport: '97'
+  }, {
+   maths: '77',
+   sport: '99'
+  }]
+ });
+ it(`converts an Array of literal objects to Array of arrays`, () => {
+  const actual = jsons2arrays(fixtures);
+  const expected = [
+   ['maths', 'sport'],
+   ['90', ''],
+   ['', '97'],
+   ['77', '99']
+  ];
+  expect(actual).toEqual(expected);
+ });
+
+ it(`converts to Array of arrays following the order of headers`, () => {
+  const actual = jsons2arrays(fixtures, ['sport', 'maths']);
+  const expected = [
+   ['maths', 'sport'].reverse(), ['90', ''].reverse(), ['', '97'].reverse(), ['77', '99'].reverse()
+  ];
+  expect(actual).toEqual(expected);
+ });
+ it(`accepts any size of headers list`, () => {
+  const headers = ['maths', 'sport', 'phy', 'ch'];
+  const actual = jsons2arrays(fixtures, headers);
+  const expected = [
+   headers, ['90', '', '', ''],
+   ['', '97', '', ''],
+   ['77', '99', '', '']
+  ];
+  expect(actual).toEqual(expected);
+ });
+
+});
+
+describe(`core::arrays2csv`, () => {
+ let fixtures;
+ beforeEach(() => {
+  fixtures = [
+   [`a`, `b`],
+   [`c`, `d`]
+  ];
+
+ });
+ it(`converts Array of arrays to string in CSV format`, () => {
+   const actual = arrays2csv(fixtures);
+   expect(actual).toBeA('string');
+   expect(actual.split(`\n`).join(`|`)).toEqual(`a,b|c,d`);
+ });
+
+ it(`renders  CSV headers whenever it was given `, () => {
+   const headers = [`X`, `Y`];
+   const firstLineOfCSV = arrays2csv(fixtures, headers).split(`\n`)[0];
+   expect(firstLineOfCSV).toEqual(headers.join(`,`));
+ });
+});
+
+
+describe(`core::jsons2csv`, () => {
+ let fixtures;
+ beforeEach(() => {
+  fixtures = [{
+   X: '88',
+   Y: '97'
+  }, {
+   X: '77',
+   Y: '99'
+  }]
+ });
+
+ it(`converts Array of literal objects to string in CSV format including headers`, () => {
+
+   const actual = jsons2csv(fixtures);
+   const expectedHeaders = ['X', 'Y'];
+   const expected =`${expectedHeaders.join(`,`)}|88,97|77,99`;
+   expect(actual).toBeA('string');
+   expect(actual.split(`\n`).join(`|`)).toEqual(expected);
+ });
+
+});