feat(calculator.ts): add tan method

Author: gfmio

src/Calculator.ts

@@ -66,4 +66,9 @@ export default class Calculator {
     this.current = Math.cos(this.current);
     return this;
   }
+
+  public tan() {
+    this.current = Math.tan(this.current);
+    return this;
+  }
 }

tests/Calculator.test.ts

@@ -4,6 +4,9 @@ import { describe, it } from "mocha";
 import Calculator from "../src/Calculator";
 
 describe("Calculator", () => {
+  it("has the correct initial value when no argument is supplied", () => expect(new Calculator().value()).equal(0));
+  it("has the correct initial value when an argument is supplied", () => expect(new Calculator(3).value()).equal(3));
+
   const calculator = new Calculator();
 
   it("can add", () => expect(calculator.add(2).value()).equal(2));
@@ -14,11 +17,9 @@ describe("Calculator", () => {
   // prettier-ignore
   it("can exp", () => expect(calculator.sub(1).exp().value()).equal(Math.E));
   it("can ln", () => expect(calculator.ln().value()).equal(1));
-
   it("can clear", () => expect(calculator.clear().value()).equal(0));
   it("can sin", () => expect(calculator.sin().value()).equal(0));
   it("can cos", () => expect(calculator.cos().value()).equal(1));
-
-  it("has the correct initial value when no argument is supplied", () => expect(new Calculator().value()).equal(0));
-  it("has the correct initial value when an argument is supplied", () => expect(new Calculator(3).value()).equal(3));
+  // prettier-ignore
+  it("can tan", () => expect(calculator.clear().tan().value()).equal(0));
 });