Writing several tests together (multiple test cases)

This lesson covers running several test cases together in VB.NET, with the aim of understanding what a body of unit tests looks like.

Listing pairs of input and expected result in advance, then comparing each against the actual result, lets you test a body of cases efficiently — and without the gaps that checking by hand leaves.

The sample code gathers the cases into an array of (a, b, expected) tuples, passes each to Add() in a For statement, checks the result, and counts how many passed. Adding a case is all it takes to add a check.

A common early stumble is testing only the ordinary cases and forgetting the boundaries. Covering the easily overlooked ones — (-1, 1, 0), (0, 0, 0) — is what matters.

In professional work, re-running every test automatically after each change — regression testing — to confirm nothing else broke is a widely adopted practice.

📖 Reference code

Function Add(a As Integer, b As Integer) As Integer
    Return a + b
End Function

Dim testCases = New (a As Integer, b As Integer, expected As Integer)() {
    (2, 3, 5),
    (-1, 1, 0),
    (0, 0, 0)
}

Dim passed As Integer = 0
For i As Integer = 0 To testCases.Length - 1
    Dim tc = testCases(i)
    Dim result As Integer = Add(tc.a, tc.b)
    Dim ok As Boolean = (result = tc.expected)
    If ok Then passed += 1
    Console.WriteLine("Test " & (i + 1) & ": " & If(ok, "OK", "NG"))
Next
Console.WriteLine(passed & "/" & testCases.Length & " passed")

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run VB.NET directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).