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PHP: How we test your solutions

Our site automatically checks your solutions. You may be wondering how it works.

In the simplest case, the system just runs the code and looks at what's displayed on the screen. Then it compares the actual output against the expected one.

In the future, more complicated lessons, you will write functions - mini-programs that take information from the external world and perform operations on it. Verifying solutions gets a little more complicated in this case. The system runs your code and passes data to it. The system knows what result a correctly written function would give with the data the system provides it with, and this result is what the system expects.

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

This is testing. It's used extensively in the real, day-to-day development process. Developers usually write the tests first, and only after that do they actually proceed to write the program itself. During that process, they run tests multiple times to check how close they are to the desired solution.

That is why our website says, “Tests passed” once you've done the exercise correctly.

Here's a simple example, say you want to print the string Hello, World!. Now imagine you make a small mistake and the function displays a different value. In that case, the system will give you the following message:

  -'Hello, World!'
  +'ello, World!'

  Tests: 1, Assertions: 1, Failures: 1.

A hint appears on the screen. The + sign on it indicates what your code printed. The - sign is what was expected. By comparing the two values, you can see the error. In the example above, you can see that the letter H is missing from the output.

In addition to our tests, it'll also be extremely useful to experiment with code. To do this, you can use Ideally, you should execute all the code in the lessons yourself.

Sometimes, it'll seem that you've done everything correctly, but the system seems to be fickle and won't make a decision. It's nigh on impossible for the system to just decide that it's wrong. Failed tests simply won't get as far as the site, they're automatically run after each change. In the vast majority of cases (all our projects have been run millions of times in total over many years) the error is in the solution code. It can be very imperceptible, maybe you used the wrong punctuation, or you used upper case instead of lower case, or you missed a comma. Other cases are more complicated. Maybe your solution works for one set of inputs, but not for another. So always read the instructions and test your output carefully. There will almost certainly be a sign of an error.

However, if you're sure there's an error or find some kind of inaccuracy, you can always point it out. At the end of each theory section, there's a link to the contents of the lesson on Github (this project is completely open-source!). You can write about an issue, look through the tests (you can see how your code is called there), and even send a pull request. If this still feels like a dark forest for you, then join our community, we'll always be there to help in the #hexlet-feedback channel.


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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 are special code that checks the programs have been made correctly by checking the correct result against the actual one.

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