<ahref="https://github.com/philsquared/Catch/releases/download/v1.8.1/catch.hpp">The latest, single header, version can be downloaded directly using this link</a>
## What's the Catch?
Catch stands for C++ Automated Test Cases in Headers and is a multi-paradigm automated test framework for C++ and Objective-C (and, maybe, C). It is implemented entirely in a set of header files, but is packaged up as a single header for extra convenience.
## How to use it
This documentation comprises these three parts:
* [Why do we need yet another C++ Test Framework?](docs/why-catch.md)
* [Tutorial](docs/tutorial.md) - getting started
* [Reference section](docs/Readme.md) - all the details
* Issues and bugs can be raised on the [Issue tracker on GitHub](https://github.com/philsquared/Catch/issues)
* For discussion or questions please use [the dedicated Google Groups forum](https://groups.google.com/forum/?fromgroups#!forum/catch-forum)
* See [who else is using Catch](docs/opensource-users.md)
Most test frameworks have a large collection of assertion macros to capture all possible conditional forms (```_EQUALS```, ```_NOTEQUALS```, ```_GREATER_THAN``` etc).
Catch is different. Because it decomposes natural C-style conditional expressions most of these forms are reduced to one or two that you will use all the time. That said there are a rich set of auxilliary macros as well. We'll describe all of these here.
Most of these macros come in two forms:
## Natural Expressions
The ```REQUIRE``` family of macros tests an expression and aborts the test case if it fails.
The ```CHECK``` family are equivalent but execution continues in the same test case even if the assertion fails. This is useful if you have a series of essentially orthogonal assertions and it is useful to see all the results rather than stopping at the first failure.
* **REQUIRE(**_expression_ **)** and
* **CHECK(**_expression_ **)**
Evaluates the expression and records the result. If an exception is thrown it is caught, reported, and counted as a failure. These are the macros you will use most of the time
CHECK( str == "string value" );
CHECK( thisReturnsTrue() );
REQUIRE( i == 42 );
* **REQUIRE_FALSE(**_expression_ **)** and
* **CHECK_FALSE(**_expression_ **)**
Evaluates the expression and records the _logical NOT_ of the result. If an exception is thrown it is caught, reported, and counted as a failure.
(these forms exist as a workaround for the fact that ! prefixed expressions cannot be decomposed).
REQUIRE_FALSE( thisReturnsFalse() );
Do note that "overly complex" expressions cannot be decomposed and thus will not compile. This is done partly for practical reasons (to keep the underlying expression template machinery to minimum) and partly for philosophical reasons (assertions should be simple and deterministic).
* `CHECK(a == 1 && b == 2);`
This expression is too complex because of the `&&` operator. If you want to check that 2 or more properties hold, you can either put the expression into parenthesis, which stops decomposition from working, or you need to decompose the expression into two assertions: `CHECK( a == 1 ); CHECK( b == 2);`
* `CHECK( a == 2 || b == 1 );`
This expression is too complex because of the `||` operator. If you want to check that one of several properties hold, you can put the expression into parenthesis (unlike with `&&`, expression decomposition into several `CHECK`s is not possible).
### Floating point comparisons
When comparing floating point numbers - especially if at least one of them has been computed - great care must be taken to allow for rounding errors and inexact representations.
Catch provides a way to perform tolerant comparisons of floating point values through use of a wrapper class called ```Approx```. ```Approx``` can be used on either side of a comparison expression. It overloads the comparisons operators to take a tolerance into account. Here's a simple example: