Decision Table

 Decision tables are compact and precise ways of modelling complicated logic we use in a computer program. They do this by mapping the different states of a program to an action that a program should perform.

It maps conditions against actions: it expresses the fact that certain actions are to be performed only if certain conditions are satisfied.

Decision table helps to check all possible combinations of conditions for testing and testers can also identify missed conditions easily.

It is a table of rows and columns, separated into four quadrants

A FEW GUIDELINES FOR CONSTRUCTING A DECISION TABLE:

1) Draw boxes for the top and bottom left quadrants.

2) List the conditions in the top left quadrant.

When possible, phrase the conditions as questions that can be answered with a Y for yes and an N for a no.

3) List the possible actions in the bottom left quadrant.

4) Count the possible values for each condition and multiply these together to determine how many unique combinations of conditions are present. Draw one column in the top and bottom right quadrants for each combination. For example, if there are two conditions and the first condition has two possible values while the second has three possible values, draw six (2 * 3) columns.

5) Enter all possible combinations of values in the columns in the top right quadrant of the table.

6) For each column, that is, each unique combination of conditions, mark an X in the bottom right quadrant in the appropriate action row. The X marks the intersection between the required action and each unique combination of condition values. If the user provides correct username and password the user will be logged in. If any of the input is wrong or blank an error message will be displayed.