Testing a program means giving it some example inputs to make sure that there are no logic errors.

A test plan should outline exactly what will be tested.

The test data from your test plan should cover all three categories of data:

• Normal data = valid data that a user is expected to input
• Boundary data = data on either side of the boundary between valid and invalid
• Erroneous data = invalid data that your program should reject

Table 1 shows an example test plan for a program which should accept a four-digit numeric input.

Table 1

Type	Input	Expected output
Normal	1234	Valid.
Boundary	0000	Valid.
Boundary	9999	Valid.
Boundary	10000	Reject: too long
Boundary	999	Reject: too short
Erroneous	12ab	Reject: not numeric

Trace tables can help you pin-point exactly what went wrong if the actual output doesn't match the expected output.

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Why is it important to test programs?

Many issues arise if your software doesn't work, including:
• Competition with other software providers
• Reputational damage
• Legal obligations
• Safety

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