Added test to ensure that plus applies any pending operation
Added test to ensure that equals applies any pending operation
Refactored operation button tess to remove duplication, revealing a subtle bug
Fixed bug where the first operand was not cleared when equals() was called
Clarified addition test to indicate it is just using integer numbers
Restructured the tests to better reveal the intent and expose redundancy
Extracted function to return the calculator display
Extracted function for remove duplication in the first operator test
Extracted function to remove duplication in the second operator test
Extracted function to remove duplication in the third operator test
Added tests for minus operator
Added call to allClear() to operator tests
Added simplest minus operator that will pass the tests
Added tests for subtraction
Implemented the subtraction operation
Added multiplyBy operation tests
Added simplest multiplyBy implementation
Added multiplication functional tests
Implemented the multiplication function
Extracted function operatorKeyPressed() with duplicate functionality from operator keys