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:
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.
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
Examples:
CHECK( str == "string value" ); CHECK( thisReturnsTrue() ); REQUIRE( i == 42 );
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).
Example:
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).
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:
REQUIRE( performComputation() == Approx( 2.1 ) );
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.
std::numeric_limits<float>::epsilon()*100
.0.0
.1.0
.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
Margin check is used only if the relative (epsilon and scale based) check fails.
Approx target = Approx(100).margin(5); 100.0 == target; // Obviously true 200.0 == target; // Obviously still false 104.0 == target; // True, because we set target to allow absolute error up to 5
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 no exception is thrown during evaluation of the expression.
Expects that an exception (of any type) is be thrown during evaluation of the expression.
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).
e.g.
REQUIRE_THROWS_WITH( openThePodBayDoors(), Contains( "afraid" ) && Contains( "can't do that" ) ); REQUIRE_THROWS_WITH( dismantleHal(), "My mind is going" );
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.
REQUIRE_NOTHROW([&](){ int i = 1; int j = 2; auto k = i + j; if (k == 3) { throw 1; } }());
To support Matchers a slightly different form is used. Matchers have their own documentation.
Matchers can be composed using &&
, ||
and !
operators.
Currently assertions in Catch are not thread safe. For more details, along with workarounds, see the section on the limitations page.