Add unit tests

.gitignore

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+# dependencies
+/node_modules
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.idea

package.json

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+{
+  "scripts": {
+    "test": "NODE_ENV=test jest"
+  },
+  "dependencies": {
+    "jest": "^28.1.1"
+  }
+}

tests.test.js

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+const getBitcoinPriceSixMonthsFromToday = () => {
+    return 58548
+}
+
+const getBitcoinPriceToday = () => {
+    return 21024
+}
+
+describe('when a user buys low', () => {
+    const initialPrice = getBitcoinPriceSixMonthsFromToday()
+
+    test('it should be able to sell high', () => {
+        const finalPrice = getBitcoinPriceToday()
+        expect(finalPrice).toBeGreaterThan(initialPrice);
+    })
+})
+
+