Week 6 - Debugging and Testing

Learning Goals

• Construct a test table with expected and actual outputs.
• Identify and select relevant test data.
• Use breakpoints in Visual Studio to step through code.
• Use Console.WriteLine as a debugging tool.

Key Concepts

Types of Test Data

Good testing covers three categories:

Category	Description	Example for a quantity field
Normal	Typical valid input	50
Boundary	Values at the edge of the allowed range	0, 1, 998, 999
Invalid	Data that should be rejected	-1, 1000, "abc", ""

Test Tables

A test table records what you expected to happen and what actually happened.

Test #	Input	Expected Output	Actual Output	Pass/Fail
1	Name "Cola", Price 3.00, Qty 24	Product added successfully	Product added successfully	Pass
2	Name ""	Error: Name cannot be blank	Error: Name cannot be blank	Pass
3	Price -5	Error: Price must be > 0	Product added	Fail
4	Qty "abc"	Error: Must be a whole number	Error: Must be a whole number	Pass

Breakpoints in Visual Studio

A breakpoint pauses the program at a chosen line so you can inspect variables and follow the code step by step.

Basic process:

1. Click in the margin beside a line number.
2. Run the program with F5.
3. Let the program pause at the breakpoint.
4. Hover over variables to inspect their values.
5. Use F10 to step through the next line.

Debugging Output Statements

You can also print temporary values while the program runs.

static double CalculateTotalValue(double[] prices, int[] quantities)
{
    double total = 0;

    for (int i = 0; i < prices.Length; i++)
    {
        double lineValue = prices[i] * quantities[i];
        Console.WriteLine($"DEBUG: item {i} = ${lineValue}");
        total += lineValue;
    }

    return total;
}

Your Task

Take your Week 5 solution and complete the following:

Part A - Build a Test Table

Design a test table with at least 8 tests covering:

• normal inputs that should succeed
• boundary values for price and quantity
• invalid inputs for all three fields

Write the test table as a comment block at the top of your program.

Part B - Run the Tests

Run your program and fill in the Actual column. Fix any failures you find.

Part C - Add a Breakpoint

Set a breakpoint inside one of your validation methods. Step through it with F10 while entering a boundary value. Write a short paragraph comment in your code describing what you observed.

Extension

• Deliberately introduce a bug into a calculation method.
• Use a breakpoint and step-through debugging to identify the exact line producing the wrong result.
• Fix the bug and note what the breakpoint revealed.

Common Mistakes to Avoid

• only testing inputs you expect to work
• skipping boundary values
• leaving debug Console.WriteLine statements in the finished program
• writing the test table after testing instead of before