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Error Guessing Technique

The test case design technique or methods or approaches that need to be followed by every test engineer while writing the test cases to achieve the maximum test coverage. If we follow the test case design technique, then it became process-oriented rather than person-oriented.

The test case design technique ensures that all the possible values that are both positive and negative are required for the testing purposes. In software testing, we have three different test case design techniques which are as follows:

  • Error Guessing
  • Equivalence Partitioning
  • Boundary Value Analysis[BVA]
Error Guessing Technique

In this section, we will understand the first test case design technique that is Error guessing techniques.

Error guessing is a technique in which there is no specific method for identifying the error. It is based on the experience of the test analyst, where the tester uses the experience to guess the problematic areas of the software. It is a type of black box testing technique which does not have any defined structure to find the error.

In this approach, every test engineer will derive the values or inputs based on their understanding or assumption of the requirements, and we do not follow any kind of rules to perform error guessing technique.

The accomplishment of the error guessing technique is dependent on the ability and product knowledge of the tester because a good test engineer knows where the bugs are most likely to be, which helps to save lots of time.

How does the error guessing technique be implemented?

The implementation of this technique depends on the experience of the tester or analyst having prior experience with similar applications. It requires only well-experienced testers with quick error guessing technique. This technique is used to find errors that may not be easily captured by formal black box testing techniques, and that is the reason, it is done after all formal techniques.

The scope of the error guessing technique entirely depends on the tester and type of experience in the previous testing involvements because it does not follow any method and guidelines. Test cases are prepared by the analyst to identify conditions. The conditions are prepared by identifying most error probable areas and then test cases are designed for them.

The main purpose of this technique is to identify common errors at any level of testing by exercising the following tasks:

  • Enter blank space into the text fields.
  • Null pointer exception.
  • Enter invalid parameters.
  • Divide by zero.
  • Use maximum limit of files to be uploaded.
  • Check buttons without entering values.

The increment of test cases depends upon the ability and experience of the tester.

Purpose of Error guessing

The main purpose of the error guessing technique is to deal with all possible errors which cannot be identified as informal testing.

  • The main purpose of error guessing technique is to deal with all possible errors which cannot be identified informal testing.
  • It must contain the all-inclusive sets of test cases without skipping any problematic areas and without involving redundant test cases.
  • This technique accomplishes the characteristics left incomplete during the formal testing.

Depending on the tester's intuition and experience, all the defects cannot be corrected. There are some factors that can be used by the examiner while using their experience -

  • Tester's intuition
  • Historical learning
  • Review checklist
  • Risk reports of the software
  • Application UI
  • General testing rules
  • Previous test results
  • Defects occurred in the past
  • Variety of data which is used for testing
  • Knowledge of AUT

Examples of Error guessing method


A function of the application requires a mobile number which must be of 10 characters. Now, below are the techniques that can be applied to guess error in the mobile number field:

  • What will be the result, if the entered character is other than a number?
  • What will be the result, if entered characters are less than 10 digits?
  • What will be the result, if the mobile field is left blank?

After implementing these techniques, if the output is similar to the expected result, the function is considered to be bug-free, but if the output is not similar to the expected result, so it is sent to the development team to fix the defects.

However, error guessing is the key technique among all testing techniques as it depends on the experience of a tester, but it does not give surety of highest quality benchmark. It does not provide full coverage to the software. This technique can yield a better result if combined with other techniques of testing.


Suppose we have one bank account, and we have to deposit some money over there, but the amount will be accepted on a particular range of which is 5000-7000. So here, we will provide the different input's value until it covers the maximum test coverage based on the error guessing technique, and see whether it is accepted or give the error message:

value description
6000 Accept
5555 Accept
4000 Error message
8000 Error message
blank Error message
100$ Error message
---- ----
---- ----
Maximum test coverage


Condition: if amount >5000 and amount<7000 amount

And, if we enter 5000 → error message (not accepted based on the condition)

7000→ error message (not accepted based on the condition)

Advantages and disadvantage of Error guessing technique


The benefits of error guessing technique are as follows:

  • It is a good approach to find the challenging parts of the software.
  • It is beneficial when we will use this technique with the grouping of other formal testing techniques.
  • It is used to enhance the formal test design techniques.
  • With the help of this technique, we can disclose those bugs which were probably identified over extensive testing; therefore, the test engineer can save lots of time and effort.


Following are the drawbacks of error guessing technique:

  • The error guessing technique is person-oriented rather than process-oriented because it depends on the person's thinking.
  • If we use this technique, we may not achieve the minimum test coverage.
  • With the help of this, we may not cover all the input or boundary values.
  • With this, we cannot give the surety of the product quality.
  • The Error guessing technique can be done by those people who have product knowledge; it cannot be done by those who are new to the product.

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