Error Guessing

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Error guessing is a proactive software testing technique employed by testers to anticipate the likelihood of errors, defects, and failures based on their knowledge and expertise, which includes factors such as the application's historical performance, common error types, and previously encountered failures in similar applications.

Determining the scope of test cases typically falls within the purview of the software tester, who leverages their expertise and intuition to identify scenarios prone to software failures or likely to trigger errors.

Table of Contents

  1. How to Implement
  2. Error Guessing Factors
  3. Example of Error Guessing
  4. Applicability
  5. Test Coverage
  6. Types of Defects
  7. Benefits of Error Guessing 
  8. Limitations of Error Guessing
  9. Video Tutorial

How to implement Error-Guessing Technique?

An organized methodology for implementing the error-guessing technique involves creating a list of potential errors, defects, and failures and designing tests to uncover these issues and identify their root causes.

These Lists can be developed through various means, including experiential knowledge, defect and failure data analysis, or a general understanding of the common causes of software failures.

Error Guessing Factors

The Error Guessing technique relies on a range of factors, including

  • historical learning
  • prior error patterns
  • failures observed in other applications
  • insights gained from previous releases
  • tester intuition
  • past defects
  • production tickets
  • review checklists
  • the application's user interface
  • prior test results
  • risk assessments of the application
  • diverse test data
  • general testing principles
  • knowledge of the Application Under Test


For instance, let us consider a situation where a Test Analyst is responsible for testing the OTP text field that accepts a six-digit input. In such a scenario, potential error-guessing test cases may include:

  • the submission of a blank field
  • Entry of non-numeric characters
  • The input of more or fewer than six digits
  • Submission of an incorrect six-digit OTP
  • Entry of an expired OTP


Error guessing is a software testing technique primarily implemented during integration and system testing, although it can be applied at any level of the testing process.

This technique is often deployed with other testing methods to expand the scope of existing test cases. 

Test Coverage

Utilizing a defect taxonomy enables the calculation of coverage by dividing the number of tested taxonomy items by the total number of taxonomy items and expressing the result as a percentage.

Without a defect taxonomy, coverage is restricted by the tester's expertise, knowledge, and available time. The number of defects detected through this technique may vary depending on the tester's ability to pinpoint the problematic areas.

Types of Defects

Typical defects during error guessing are those either specified in the defect taxonomy or identified by the Test Analyst through intuitive guesswork that may not have been uncovered via black-box testing.

Benefits of Error Guessing

The error-guessing technique offers several benefits, including:

  • Enhance formal test design techniques: When implemented in conjunction with other formal testing methods. 
  • Save time and effort: Additionally, utilizing this technique enables the efficient discovery of bugs that may have been missed during extensive testing, saving valuable time and effort for the test engineer.
  • Essential for Risk Analysis: Besides its function as a testing technique, Error guessing can be an essential tool to identify potential failure modes during risk analysis. 
  • Effective for New Software: Lastly, Error guessing can be an effective method for testing new software releases, allowing the early identification of common defects before engaging in more rigorous and systematic testing.

Limitations of Error Guessing

Despite its usefulness, the error-guessing technique has limitations and difficulties:

  • Challenging assessment of test coverage: One such limitation is the difficulty in assessment of test coverage due to the Test Analyst's variation in capability and experience.
  • Person-Oriented: Moreover, the technique is person-oriented and requires an experienced tester familiar with the common defects that are often introduced in the type of code being tested.
  • Less Reproducible: It is commonly used but frequently not documented and may be less reproducible than other forms of testing.
  • Not Properly Documented: Test cases may be documented in a way only the author understands and can reproduce.
  • Not Sufficient Alone:  Furthermore, it's essential to remember that error guessing is not a substitute for formal testing techniques. Instead, it should be used with other formal techniques where possible and only when the tester has experience with similar applications.