why I need testings in rails?

} All the time I hear that RoR has great testing enviroment.
} Well, why I need tests? I test my webapp all the time - code a page and
} than test it. So why I need that extra test - does it make some special
} tests?
} I am confused

Different languages and frameworks offer different tradeoffs, among them
being different safety nets.

C++ provides strong type safety in its duck typing (yes, the C++ templating
language supports duck typing) that guarantees (unsafe casting aside) that
if your program compiles then there is code backing all method calls, not
to mention excellent runtime performance. On the other hand, it allows
arbitrary memory access, requires manual memory management, requires many
more lines of code as compared to a language like Ruby to accomplish
similar tasks, and the extent of the running code is fixed at compile time
modulo explicit plugin interfaces.

There is still value to automated tests (and assertions!) in C++, but many
of the sorts of tests that are important for Ruby code occur implicitly at
compile time; the compiler is a static code analyzer, and the code itself
provides sufficient information to support this analysis.

Ruby is sufficiently dynamic in a number of senses (e.g. loading code can
alter existing code paths), which precludes such static analysis. To regain
a level of certainty that the code works after a seemingly minor change,
one writes tests that assert preconditions and postconditions and results
and failure modes and such. Running those automated tests is similar to
performing the static analysis that the C++ compiler performs. While it is
possible to run Ruby code that has not undergone such automated testing, it
is best to consider it similar to trying to run C++ code without compiling
it. (Sadly, I am routinely guilty of this.)

} pete