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PHP: How do we verify solutions?

Our website verifies your solutions automatically. You may wonder how it works.

In the simplest case the system runs your code and analyzes the screen output. Then it compares the actual output against the expected output.

The following lessons deal with more complex matters. You will be writing functions: a kind of mini-programs that receive some data from outside and perform operations on it. Verifying solutions gets a little more complicated in that case. The system runs your code sending some data to it. The system knows what result a correctly written function would receive with that particular data and "expects" it.

Let's assume your task is to program a function that adds two numbers. The verification system would give it several combinations of numbers and compare your function's answers with correctly calculated ones. If all actual values match the expected ones, your solution would be considered valid.

This approach is named testing. It is used extensively in the real life day-to-day development process. A developer usually writes tests first, and only after proceeds to writing the program itself. During that process he runs tests multiple times to check how close he got to the desired solution.

That is why our website says “Tests passed” once you solved the task correctly.

One of your tasks in the following lessons will be to write a function that performs certain calculations and returns the result. As an example, let's assume you made a small mistake and the function returned a wrong value. In that case, the system will give you the following message:

Fatal error: Uncaught Assert\InvalidArgumentException: Value "10" does not equal expected value "35".

The main thing comes after the colon: “Value ‘10’ does not equal expected value ‘35’”. This means the correctly designed function would have returned 35, and yet the current function returns 10 — which means it works incorrectly.


Print the following to screen: 9780262531962.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.



  • Tests - code designed to check if a program works correctly; it does so by comparing a set of known valid results against the actual output of the program.

If you got stuck and don't know what to do, you can ask a question in our huge and friendly community