Choosing Test Data

In system testing, test data should cover the possible values of each parameter based on the the requirements. Since testing every value is impractical, a few values should be chosen from each equivalence class. An equivalence class is a set of values that should all be treated the same.

Ideally, test cases that check error conditions are written separately from the functional test cases and should have steps to verify the error messages and logs. Realistically, if error test cases are not yet written, it is OK for testers to check for error conditions when performing normal functional test cases. It should be clear which test data, if any, is expected to trigger errors.

Example equivalence classes:

Strings

• empty string
• String consisting solely of white space
• String with leading or trailing white space
• syntactically legal: short and long values
• syntactically legal: semantically legal and illegal values
• syntactically illegal value: illegal characters or combinations
• Make sure to test special characters such as #, ", ', &, and <
• Make sure to test "Foreign" characters typed on international keyboards

Numbers

• empty string, if possible
• 0
• in range positive, small and large
• in range negative, small and large
• out of range positive
• out of range negative
• with leading zeros
• syntactically invalid (e.g., includes letters)

Identifiers

• empty string
• syntactically legal value
• syntactically legal: reference to existing ID, invalid reference
• syntactically illegal value

Radio buttons

• one item checked
• nothing checked, if possible

Checkboxes

• checked
• unchecked

Drop down menus

• select each item in turn

Scrolling Lists

• select no item, if possible
• select each item in turn
• select combinations of items, if possible
• select all items, if possible

File upload

• blank
• 0 byte file
• long file
• short file name
• long file name
• syntactically illegal file name, if possible (e.g., "File With Spaces.tar.gz")