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Testing Invalid Data

Testing Invalid Data
Testing Invalid Data

Invalid data inputs that break a text box are:


  • blank line;
  • invalid numeric data (e.g., negative or fractional in cases where they’re useless);
  • invalid format (for example, for a date or phone in cases where they’re useless);
  • invalid printable characters (service or national symbols);
  • invalid non-printable characters (line feed or tab).


Example. We have some web application for testing, which is available at a specific Internet address.


  1. At the first stage it became clear that there were no documentary requirements.


  1. Exploratory testing reveals that the program is designed to create mailboxes, the interface has three text input fields: email, password, the size of the box in MB and the Submit button.


  1. Basic scenarios (CRUD operations)

There is only the Create operation. There are no READ, UPDATE and DELETE operations (retrieving information about the mailbox, editing and deleting the mailbox). It makes sense to write a bug or ask the authoritative person of the project why these are absent.

You need to create a box and make sure that it really works.


  1. Analysis of trends – find out what the maximum allowed size for the mailbox is.


  1. Unit testing of input data


5.1. There are three input fields.

5.2. Equivalence classes of valid values:


Email accounts can be


  1. Busy / free.
  2. On the domain that is serviced / not serviced by this server.


In total, 4 equivalence classes are obtained. Text input of an occupied E-mail should be checked during this stage because value is valid E-mail according to RFC. It is impossible to consider this value as erroneous and to postpone testing for the last stage.


The password can meet complexity requirements or not – grade 2.


If we know the detailed password complexity requirements (for example, from the validator message), there may be more equivalence classes here – the password is of incorrect length, or does not use the necessary number of symbols, letters or numbers, etc.


The size can be


  1. Less than the allowable limit / exceeds the allowable limit.
  2. Integer  / fractional.


Four equivalence classes


The negative size is invalid (it is meaningful), we will test it at the final stage.

In total, 10 tests are obtained.


  1. Combining input data


  • email: busy, free, our domain, external domain;
  • password: safe, not safe;
  • size: less than limit, more than limit, integer, fractional;
  • total combinations 4 * 2 * 4 = 32.


We use the utility PICT, it will give us 17 pairwise combinations.


  1. Boundary value analysis


  • email: data range – not applicable;
  • length of data – before the dog at least 1 character should be, as a maximum – 64 (Wikipedia);
  • you need to check: 0, 1, 64, 65;
  • the total length is 254 maximum (check 254 and 255).

You are welcome to use assurance testing services if your development products do not fully satisfy the target audience. Close interaction with qa professionals will lead you to success.

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