Add Kilometers/Hour to Miles/Hour conversion and reverse

test/kphToMph/kphToMph.js

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+const kphToMph = (kph) => 0.621371192 * kph;
+module.exports = kphToMph;

test/kphToMph/kphToMph.test.js

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+const expect = require('expect');
+const kphToMph = require('./kphToMph.js');
+
+test('kphToMph is a Function', () => {
+  expect(kphToMph).toBeInstanceOf(Function);
+});
+test('Returns mph from kph.', () => {
+  expect(kphToMph(10)).toBe(6.21371192);
+});
+test('Returns mph from kph.', () => {
+  expect(kphToMph(345.4)).toBe(214.62160971679998);
+});

test/mphToKph/mphToKph.js

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+const mphToKph = (mph) => 1.6093440006146922 * mph;
+module.exports = mphToKph;

test/mphToKph/mphToKph.test.js

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+const expect = require('expect');
+const mphToKph = require('./mphToKph.js');
+
+test('mphToKph is a Function', () => {
+  expect(mphToKph).toBeInstanceOf(Function);
+});
+test('Returns kph from mph.', () => {
+  expect(mphToKph(10)).toBe(16.09344000614692);
+});
+test('Returns kph from mph.', () => {
+  expect(mphToKph(85.9)).toBe(138.24264965280207);
+});