Writing Conditionals and Practicing TDD

1. Writing Conditionals and Practicing TDD

2. TDD Refresher • RED – write the test and watch it fail • Why do we watch it fail? • GREEN – write the simplest code that can make it pass • REFACTOR – cleanup • comments • variable names • eliminate duplication (pay attention to duplication between the values the test knows and the values the code knows)

3. Chapter Project • This chapter’s project is a tax calculator • You will write a series of methods that make a series of tests pass. • The goal is to practice writing conditional statements

4. If Statements • Used when we want something to happen only under certain conditions condition if(potatoNumber != 4) { System.out.print(" potato"); } then block

5. if-then-else Statements • Used when we want to choose between two different behaviors long result = oneBack + twoBack; if (result < oneBack) { oneBack = 1; twoBack = 0; result = 1; } else { twoBack = oneBack; oneBack = result; } condition then block else block

6. Why have the curly brackets? • Exactly one statement after the condition is considered to be inside the condition • Those brackets make one statement out of a sequence of statements if(potatoNumber != 4) { System.out.print(" potato"); halfway = true; }

7. Watch the semi-colon • What will this code do? notice the semi-colon if(potatoNumber != 4); { System.out.print(" potato"); } That semi-colon ends the one statement in the then block, so the rest of the code is NOT part of the if statement (and will always be executed).

8. Testing Conditionals • Clearly, we cannot test every value that a system might see, so we need to target our tests on values that are likely to cause errors. • Border case - A situation where a small change in input causes a fundamentally different behavior. • Focus the tests on the values around that situation because those are the values where we are most likely to have a defect

9. Nested Conditionals if (grade > 90) { System.out.println("Excellent"); } else { if (grade > 80) { System.out.println("Average"); } else { System.out.println("Poor"); } } What is the output for 95? 85? 75? 90? 80? What are the border cases?