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24 Sep, 2024

White Box Testing - Its Techniques and Types

Posted on 24 Sep, 2024 by Vatsal, Posted in Blog

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In this blog, we’ll deal with one of the most popular methods of testing a system or system component thoroughly – namely, white box testing.

What is White Box Testing?

White box testing refers to a scenario where, the tester deeply understands the inner workings of the system or system component being tested.

Gaining a deep understanding of the system or component is possible when the tester understands these at program- or code-level. So almost all the time, the tester needs to either understand or have access to the source code that makes up the system – usually in the form of specification documents.

This is also known as structural testing as the tester chooses which inputs to test and follows their paths through the software to reach their expected outputs.

White box testing is used in the unit, integration and systems phases of software testing. Since the code is visible it is also called as open box/ glass box/ transparent box testing.

The smallest unit of software is one line of the code since developers are testing that each and every line so it is called as unit testing also.

key principles

The key principles that assist you in executing white box tests successfully are:

  • Statement Coverage – ensure every single line of code is tested.
  • Branch Coverage – ensure every branch (e.g. true or false) is tested.
  • Path Coverage – ensure all possible paths are tested.

White Box Testing Tools

White box testing is a type of testing where the tester can see the code. The main purposes of this type of testing are to test the inner workings of the software, as well as strengthen its security, and improve its usability and design.

Here are some of the top white box testing tools to use:

  • Veracode
  • Parasoft Jtest
  • EclEmma
  • CppUnit
  • NUnit
  • RCUNIT

What Does White Box Testing Focus On?

  • Path Checking: Examines the different routes the program can take when it runs. Ensures that all decisions made by the program are correct, necessary, and efficient.
  • Output Validation: Tests different inputs to see if the function gives the right output each time.
  • Security Testing: Uses techniques like static code analysis to find and fix potential security issues in the software. Ensures the software is developed using secure practices.
  • Loop Testing: Checks the loops in the program to make sure they work correctly and efficiently. Ensures that loops handle variables properly within their scope.
  • Data Flow Testing: Follows the path of variables through the program to ensure they are declared, initialized, used, and manipulated correctly.

Types of White Box Testing

White box testing can be done for different purposes. The three main types are:

  1. Unit Testing
  2. Integration Testing
  3. Regression Testing

Unit Testing

  • Checks if each part or function of the application works correctly.
  • Ensures the application meets design requirements during development.

Integration Testing

  • Examines how different parts of the application work together.
  • Done after unit testing to make sure components work well both alone and together.

Regression Testing

  • Verifies that changes or updates don’t break existing functionality.
  • Ensures the application still passes all existing tests after updates.

White Box Testing Techniques

One of the main benefits of white box testing is that it allows for testing every part of an application. To achieve complete code coverage, white box testing uses the following techniques:

1. Statement Coverage

In this technique, the aim is to traverse all statements at least once. Hence, each line of code is tested. In the case of a flowchart, every node must be traversed at least once. Since all lines of code are covered, it helps in pointing out faulty code.

2. Branch Coverage

In this technique, test cases are designed so that each branch from all decision points is traversed at least once. In a flowchart, all edges must be traversed at least once.

3. Condition Coverage

In this technique, all individual conditions must be covered as shown in the following example:

  • READ X, Y
  • IF(X == 0 || Y == 0)
  • PRINT ‘0’
  • #TC1 – X = 0, Y = 55
  • #TC2 – X = 5, Y = 0

4. Multiple Condition Coverage

In this technique, all the possible combinations of the possible outcomes of conditions are tested at least once. Let’s consider the following example:

  • READ X, Y
  • IF(X == 0 || Y == 0)
  • PRINT ‘0’
  • #TC1: X = 0, Y = 0
  • #TC2: X = 0, Y = 5
  • #TC3: X = 55, Y = 0
  • #TC4: X = 55, Y = 5

5. Basis Path Testing

In this technique, control flow graphs are made from code or flowchart and then Cyclomatic complexity is calculated which defines the number of independent paths so that the minimal number of test cases can be designed for each independent path. Steps:

  • Make the corresponding control flow graph
  • Calculate the cyclomatic complexity
  • Find the independent paths
  • Design test cases corresponding to each independent path
  • V(G) = P + 1, where P is the number of predicate nodes in the flow graph
  • V(G) = E – N + 2, where E is the number of edges and N is the total number of nodes
  • V(G) = Number of non-overlapping regions in the graph
  • #P1: 1 – 2 – 4 – 7 – 8
  • #P2: 1 – 2 – 3 – 5 – 7 – 8
  • #P3: 1 – 2 – 3 – 6 – 7 – 8
  • #P4: 1 – 2 – 4 – 7 – 1 – . . . – 7 – 8

6. Loop Testing

Loops are widely used and these are fundamental to many algorithms hence, their testing is very important. Errors often occur at the beginnings and ends of loops.

  • Simple loops: For simple loops of size n, test cases are designed that:
  1. Skip the loop entirely
  2. Only one pass through the loop
  3. 2 passes
  4. m passes, where m < n
  5. n-1 and n+1 passes
  • Nested loops: For nested loops, all the loops are set to their minimum count, and we start from the innermost loop. Simple loop tests are conducted for the innermost loop and this is worked outwards till all the loops have been tested.
  • Concatenated loops: Independent loops, one after another. Simple loop tests are applied for each. If they’re not independent, treat them like nesting.

Process of White Box Testing

  1. Input: Requirements, Functional specifications, design documents, source code.
  2. Processing: Performing risk analysis to guide through the entire process.
  3. Proper test planning: Designing test cases to cover the entire code. Execute rinse-repeat until error-free software is reached. Also, the results are communicated.
  4. Output: Preparing the final report of the entire testing process.

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