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.
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.
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
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).
Examples:
*`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).
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:
This way `Approx` is constructed with reasonable defaults, covering most simple cases of rounding errors. If these are insufficient, each `Approx` instance has 3 tuning knobs, that can be used to customize it for your computation.
* __epsilon__ - epsilon serves to set the percentage by which a result can be erroneous, before it is rejected. By default set to `std::numeric_limits<float>::epsilon()*100`.
* __margin__ - margin serves to set the the absolute value by which a result can be erroneous before it is rejected. By default set to `0.0`.
* __scale__ - scale serves to adjust the base for comparison used by epsilon, can be used when By default set to `1.0`.
#### epsilon example
```cpp
Approx target = Approx(100).epsilon(0.01);
100.0 == target; // Obviously true
200.0 == target; // Obviously still false
100.5 == target; // True, because we set target to allow up to 1% error
Scale can be useful if the computation leading to the result worked on different scale, than is used by the results (and thus expected errors are on a different scale than would be expected based on the results alone).
Expects that an exception of the _specified type_ is thrown during evaluation of the expression. Note that the _exception type_ is extended with `const&` and you should not include it yourself.
Expects that an exception is thrown that, when converted to a string, matches the _string_ or _string matcher_ provided (see next section for Matchers).
Expects that exception of _exception type_ is thrown and it matches provided matcher (see next section for Matchers).
_Please note that the `THROW` family of assertions expects to be passed a single expression, not a statement or series of statements. If you want to check a more complicated sequence of operations, you can use a C++11 lambda function._
