For this app, you'll bulid a simple, basic calculator. The difference, is that you'll be using Test Driven design to do it.

You will also not be building a UI for this as we will be using TDD to do that for the next assignment.

1. Build a Calculator class with an empty constructor and a method called addSymbol or something to that effect which accepts and returns a string. For now it will just return the accepted string.

Don't implement this now, but This method will be called when a symbol button is pressed (number or decimal), it will add that symbol to its internal member tracking the number entered into the calculator and then return a string representation of that number to be displayed

2. Write 2 tests, 1 to test if the method works when used once to add a single character when nothing else has been added, and 1 to test when multiple consecutive strings are added. Run the tests.

The first test should pass, but the second test should fail.

3. Implement that method in your calculator class.
4. Continue in this manner. Build a test for a step you want to perform, say, adding a decimal. Think of all the potential use cases to cover ie: adding a single decimal, what if the number already has a decimal. Since the Calculator is part of a separate class, it shouldn't manipulate any UI instead, return the desired string to be displayed.

This calculator should have the following features:

• Add numbers (in the future, you'll add them with buttons 0-9), but for now, just call the methods manually
• Add a decimal to the current number
• Remove the most recently added character (backspace)
• Perform the following calculations
  • Addition
  • Subraction
  • Multiplication
  • Division
• Perform repeated calculations (5 * 10 = 50, pressing equals again should return 500, etc.)
• Clear all values

Be sure to add test cases for each use case on each feature before implementing that feature

• Add more functions to your calculator (square, square root, pi)