Structured Based or White Box Testing Techniques

In previous article Software Testing Techniques,  I have explained about the testing techniques overview.

In this article we will discuss about Specification Based Testing or White Box test techniques

White-box testing

• In white box testing, an input must still produce the correct result in order to pass, but now we are also concerned with whether or not the process worked correctly.  
• “Testing based on an analysis of the internal structure of the component or system.” [ISTQB Glossary]

White-box test design technique:

• “Procedure to derive and/or select test cases based on an analysis of the internal structure of a component or system.” [ISTQB Glossary]

Following are the white box test design techniques

1. Statement Testing
2. Decision Testing
3. Condition Testing
4. Multiple Condition Testing

Statement Testing

Ref: Software Engineering Competence Center

Coverage Items:

• Executable Code Statement

Structure Element:

• Code Statement

Coverage Measure:

• All executable statements must be exercised at least once during test case execution

Thoroughness:

• The minimum level of analysis of code coverage. Does not consider different statement combinations or execution paths.

Consider the following code sample:
READ income;
tax_perc = 0.15;
IF income < 5000 THEN
tax_perc = 0;
END IF;
tax_amt = income * tax_perc;

Test Case 1: income = 6000, statement coverage = (4 / 5) *100 = 80%
Test Case 2: income = 3000, statement coverage = (5 / 5) *100 = 100%
One test case is enough to achieve 100% code coverage for this code.

Exercise: what is the minimum number of test cases to achieve 100% statement coverage for the following code:

READ income;
IF income < 5000 THEN
tax_perc = 0;
ELSE
tax_perc = 0.15;
END IF;
tax_amt = income * tax_perc;
 

No single test case is enough to achieve 100% code coverage for this code. At least two test case are needed (e.g. income = 2000, income = 7000)

Decision Testing

Coverage Items:

• Decision outcomes

Structure Element:

• IF statement, Loop control (DO-WHILE, REPEAT-UNTIL), CASE statement

Coverage Measure:

• All decision outcomes must be exercised at least once during test case execution

Thoroughness:

• Stronger than statement coverage. 100% decision coverage guarantees 100% statement coverage but not vice versa.

Consider the previous code sample:
READ income;
tax_perc = 0.15;
IF income < 5000 THEN
tax_perc = 0;
END IF;
tax_amt = income * tax_perc;

Test Case 2: income = 3000,
Statement coverage = 100%
Decision coverage = (1 / 2) * 100 = 50%

A possible defect overlooked by this test case is when the READ statement doesn't work causing the IF statement to always give TRUE.

Two test cases are necessary to achieve 100% decision coverage (e.g. 3000, 6000)