Catch2 event listeners

Catch2 is great testing library for C++ allows writing tests in C++ way which can be further adjusted to fulfill your neeeds. Today I will talk about event listeners in Catch, but let’s first start with some code sample event_listener

#define CATCH_CONFIG_MAIN
#include <catch.hpp>

TEST_CASE("A") {
	SECTION("A.1") {}
	SECTION("A.2") {}
}

TEST_CASE("B") {
	REQUIRE(true);
}

The output of event_listener program is

$ ./event_listener 
===============================================================================
All tests passed (1 assertion in 2 test cases)

By default Catch only creates overall result at the end of testing, but let’s say we want Catch to print test name at the beginning of each test (for easier debugging).

We can use event listeners for that job! All we need to do is derive from TestEventListenerBase class and override event functions we are interested (in our case testCaseStarting and sectionStarting) this way

namespace Catch {

struct custom_listener : TestEventListenerBase {
	using TestEventListenerBase::TestEventListenerBase;

	void testCaseStarting(TestCaseInfo const & info) override {
		TestEventListenerBase::testCaseStarting(info);
		stream << "test '" << info.name << "'\n";
	}

	void sectionStarting(SectionInfo const & info) override {
		TestEventListenerBase::sectionStarting(info);
		stream << "section '" << info.name << "'\n";
	}
};

CATCH_REGISTER_LISTENER(custom_listener)

}  // Catch

which creates output like

$ ./event_listener 
test 'A'
section 'A'
section 'A.1'
section 'A'
section 'A.2'
test 'B'
section 'B'
===============================================================================
All tests passed (1 assertion in 2 test cases)

See full event_listener.cpp sample implementation on github.