103 lines
3.6 KiB
Markdown
103 lines
3.6 KiB
Markdown
# Matchers
|
|
|
|
Matchers are an alternative way to do assertions which are easily extensible and composable.
|
|
This makes them well suited to use with more complex types (such as collections) or your own custom types.
|
|
Matchers were first popularised by the [Hamcrest](https://en.wikipedia.org/wiki/Hamcrest) family of frameworks.
|
|
|
|
## In use
|
|
|
|
Matchers are introduced with the `REQUIRE_THAT` or `CHECK_THAT` macros, which take two arguments.
|
|
The first argument is the thing (object or value) under test. The second part is a match _expression_,
|
|
which consists of either a single matcher or one or more matchers combined using `&&`, `||` or `!` operators.
|
|
|
|
For example, to assert that a string ends with a certain substring:
|
|
|
|
```c++
|
|
std::string str = getStringFromSomewhere();
|
|
REQUIRE_THAT( str, EndsWith( "as a service" ) );
|
|
```
|
|
|
|
The matcher objects can take multiple arguments, allowing more fine tuning.
|
|
The built-in string matchers, for example, take a second argument specifying whether the comparison is
|
|
case sensitive or not:
|
|
|
|
```c++
|
|
REQUIRE_THAT( str, EndsWith( "as a service", Catch::CaseSensitive::No ) );
|
|
```
|
|
|
|
And matchers can be combined:
|
|
|
|
```c++
|
|
REQUIRE_THAT( str,
|
|
EndsWith( "as a service" ) ||
|
|
(StartsWith( "Big data" ) && !Contains( "web scale" ) ) );
|
|
```
|
|
|
|
## Built in matchers
|
|
Currently Catch has some string matchers and some vector matchers.
|
|
The string matchers are `StartsWith`, `EndsWith`, `Contains` and `Equals`. Each of them also takes an optional second argument, that decides case sensitivity (by-default, they are case sensitive).
|
|
The vector matchers are `Contains`, `VectorContains` and `Equals`. `VectorContains` looks for a single element in the matched vector, `Contains` looks for a set (vector) of elements inside the matched vector.
|
|
|
|
|
|
## Custom matchers
|
|
It's easy to provide your own matchers to extend Catch or just to work with your own types.
|
|
|
|
You need to provide two things:
|
|
1. A matcher class, derived from `Catch::MatcherBase<T>` - where `T` is the type being tested.
|
|
The constructor takes and stores any arguments needed (e.g. something to compare against) and you must
|
|
override two methods: `match()` and `describe()`.
|
|
2. A simple builder function. This is what is actually called from the test code and allows overloading.
|
|
|
|
Here's an example for asserting that an integer falls within a given range
|
|
(note that it is all inline for the sake of keeping the example short):
|
|
|
|
```c++
|
|
// The matcher class
|
|
class IntRange : public Catch::MatcherBase<int> {
|
|
int m_begin, m_end;
|
|
public:
|
|
IntRange( int begin, int end ) : m_begin( begin ), m_end( end ) {}
|
|
|
|
// Performs the test for this matcher
|
|
virtual bool match( int const& i ) const override {
|
|
return i >= m_begin && i <= m_end;
|
|
}
|
|
|
|
// Produces a string describing what this matcher does. It should
|
|
// include any provided data (the begin/ end in this case) and
|
|
// be written as if it were stating a fact (in the output it will be
|
|
// preceded by the value under test).
|
|
virtual std::string describe() const {
|
|
std::ostringstream ss;
|
|
ss << "is between " << m_begin << " and " << m_end;
|
|
return ss.str();
|
|
}
|
|
};
|
|
|
|
// The builder function
|
|
inline IntRange IsBetween( int begin, int end ) {
|
|
return IntRange( begin, end );
|
|
}
|
|
|
|
// ...
|
|
|
|
// Usage
|
|
TEST_CASE("Integers are within a range")
|
|
{
|
|
CHECK_THAT( 3, IsBetween( 1, 10 ) );
|
|
CHECK_THAT( 100, IsBetween( 1, 10 ) );
|
|
}
|
|
```
|
|
|
|
Running this test gives the following in the console:
|
|
|
|
```
|
|
/**/TestFile.cpp:123: FAILED:
|
|
CHECK_THAT( 100, IsBetween( 1, 10 ) )
|
|
with expansion:
|
|
100 is between 1 and 10
|
|
```
|
|
|
|
---
|
|
|
|
[Home](Readme.md) |