Decision Table Based Testing

• Decision table is based on logical relationships just as the truth table.

• Decision Table is a tool that helps us look at the combination of conditions– Completeness of conditions– Inconsistency of conditions

Components of a Decision Table

C1

C2

C3

a1

a2

a3

a4

a5

T T T T F F F F

T T F F T T F F

T F T F T F T F

x x x x

x x

x x

x x x x

x x

conditions

actions

values of conditions

actions taken

R1 R2 R3 R4 R5 R6 R7 R8

rules

Read a Decision Table by columns of rules : R1 says when all conditions are T, then actions a1, a2, and a5 occur

Conditions in Decision Table

• The conditions in the decision table may take on any number of values. When it is binary, then the decision table conditions are just like a truth table set of conditions.

• The decision table allows the iteration of all the combinations of values of the condition, thus it provides a “completeness check.”

• The conditions in the decision table may be interpreted as the inputs of the table, and the actions may be thought of as outputs of the table.

How do you decide how many rules must exist ----- use this to check against Requirements Doc.?

Conditions?

• While you get the conditions from the requirement statements, what exactly do you look for?

– Requirement statement that talks about inputs– Requirement statement that talks about processing– Requirement statement that talks about outputs– Requirement statement that talks about criteria

Triangle Problem Example (“short” form)

1. a < b + c2. b < a + c3. c < a + b

4. a = b5. a = c6. b = c

1. Not triangle

1. Scalene2. Isosceles3. Equilateral4. “impossible”

F T T T T T T T T T T - F T T T T T T T T T- - F T T T T T T T T

- - - T T T T F F F F- - - T T F F T T F F- - - T F T F T F T F

X X X

X X X X X X X X Note the

Impossible cases

Pick input set, <a, b, c>, for each of the columns, or rules, belowAssume a, b and c are

all between 1 and 200R1 R2 R3 R4 R5 R7R6 R9R8 R11R10

Explain?

How Many Test Cases for Triangle Problem?

• There is the “invalid” situation --- Not a Triangle:

1. There are 3 test conditions in the Decision table2. Note the “-” entries, which represents “don’t care,” when it is

determined that the input sides <a, b, c> do not form a triangle

• There is the “valid” situation ---- A Triangle:1. There are 3 types of valid; so there are 23 = 8 test conditions 2. But there are 3 “impossible” situations3. So there are only 8 – 3 = 5 test conditions

• So, for valid values of a, b, and c, we need to come up with 8 sets of <a, b, c> to test the (3 + 5) = 8 test conditions.

Also, note that as we logically thought through this, it made us “look at’ the Requirement statement s more carefully.

Calendar Next-Date Problem

• The Calendar next-date problem has many constraints, one of which deals with the value of the month:

– Condition 1 : 1 <= month <= 12– Condition 2 : month < 1– Condition 3 : month > 12

A Decision Table for Next-Date

Condition 1

Condition 2

Condition 3

Month input

T T T T F F F F

T T F F T T F F

T F T F T F T F

There are 23 = 8 test conditions (8 columns) for the month value. But ------- are these really “independent” conditions ?

Decision Table for Next-Date

Condition 1

Condition 2

Condition 3

Month input

T T T T F F F F

T T F F T T F F

T F T F T F T F

Remember :

Condition 1: 1 < = m <= 12Condition 2: m < 1Condition 3: m > 12

R1 R2 R3 R4 R5 R6 R7 R8

Note that:a) If condition 1 is true, then conditions 2 and 3 must both be false. So Rules 1 – 4 is reduced to just R4.b) If condition 1 is false, then only one of the conditions 2 / 3, not both, can be true. So, rule R5 can be eliminated.c) Not all three conditions can be false. So rule R8 can be eliminated.

That leaves only 3 conditions ---- R4, R6, and R7 (resembles “exclusive OR” ?! )

√ √√

Decision Table for Next-Date with Actions

Condition 1

Condition 2

Condition 3

Month input

T T T T F F F F

T T F F T T F F

T F T F T F T F

Remember :

Condition 1: 1 < = m <= 12Condition 2: m < 1Condition 3: m > 12

R1 R2 R3 R4 R5 R6 R7 R8

√ √√

Action 1

Action 2

- - - X - X X -

- - X X - - - -

Note that R3 has an action defined in the Decision Table. This should trigger a question because the condition can not happen. There should be no action defined for R3 ---- perhaps, a Specification error ?

Assume actions defined in the requirements doc.

Advantages/Disadvantages of Decision Table

• Advantages:1. Allow us to start with a “complete” view, with no

consideration of dependence2. Allow us to look at and consider “dependence,”

“impossible,” and “not relevant” situations and eliminate some test cases.

3. Allow us to detect potential error in our Specifications

• Disadvantages:1. Need to decide (or know) what conditions are

relevant for testing - - - this may require Domain knowledge• e.g. need to know leap year for “next date” problem in

the book

2. Scaling up can be massive: 2n rules for n conditions - - - that’s if the conditions are binary