Reporters are a customization point for most of Catch2's output, e.g. formatting and writing out assertions (whether passing or failing), sections, test cases, benchmarks, and so on.
Catch2 comes with a bunch of reporters by default (currently 8), and you can also write your own reporter. Because multiple reporters can be active at the same time, your own reporters do not even have to handle all reporter event, just the ones you are interested in, e.g. benchmarks.
You can see which reporters are available by running the test binary
with --list-reporters. You can then pick one of them with the -r,
--reporter option, followed
by the name of the desired reporter, like so:
--reporter xml
You can also select multiple reporters to be used at the same time. In that case you should read the section on using multiple reporters to avoid any surprises from doing so.
Support for having multiple parallel reporters was introduced in Catch2 3.0.1
Catch2 supports using multiple reporters at the same time while having them write into different destinations. The two main uses of this are
- having both human-friendly and machine-parseable (e.g. in JUnit format) output from one run of binary
- having "partial" reporters that are highly specialized, e.g. having one reporter that writes out benchmark results as markdown tables and does nothing else, while also having standard testing output separately
Specifying multiple reporter looks like this:
--reporter JUnit::out=result-junit.xml --reporter console::out=-::colour-mode=ansi
This tells Catch2 to use two reporters, JUnit reporter that writes
its machine-readable XML output to file result-junit.xml, and the
console reporter that writes its user-friendly output to stdout and
uses ANSI colour codes for colouring the output.
Using multiple reporters (or one reporter and one-or-more event listeners) can have surprisingly complex semantics when using customization points provided to reporters by Catch2, namely capturing stdout/stderr from test cases.
As long as at least one reporter (or listener) asks Catch2 to capture stdout/stderr, captured stdout and stderr will be available to all reporters and listeners.
Because this might be surprising to the users, if at least one active
reporter is non-capturing, then Catch2 tries to roughly emulate
non-capturing behaviour by printing out the captured stdout/stderr
just before testCasePartialEnded event is sent out to the active
reporters and listeners. This means that stdout/stderr is no longer
printed out from tests as it is being written, but instead it is written
out in batch after each runthrough of a test case is finished.
You can also write your own custom reporter and tell Catch2 to use it. When writing your reporter, you have two options:
- Derive from
Catch::ReporterBase. When doing this, you will have to provide handling for all reporter events. - Derive from one of the provided utility reporter bases in Catch2.
Generally we recommend doing the latter, as it is less work.
Apart from overriding handling of the individual reporter events, reporters have access to some extra customization points, described below.
Catch2 currently provides two utility reporter bases:
Catch::StreamingReporterBaseCatch::CumulativeReporterBase
StreamingReporterBase is useful for reporters that can format and write
out the events as they come in. It provides (usually empty) implementation
for all reporter events, and if you let it handle the relevant events,
it also handles storing information about active test run and test case.
CumulativeReporterBase is a base for reporters that need to see the whole
test run, before they can start writing the output, such as the JUnit
and SonarQube reporters. This post-facto approach requires the assertions
to be stringified when it is finished, so that the assertion can be written
out later. Because the stringification can be expensive, and not all
cumulative reporters need the assertions, this base provides customization
point to change whether the assertions are saved or not, separate for
passing and failing assertions.
Generally we recommend that if you override a member function from either of the bases, you call into the base's implementation first. This is not necessarily in all cases, but it is safer and easier.
Writing your own reporter then looks like this:
#include <catch2/reporters/catch_reporter_streaming_base.hpp>
#include <catch2/catch_test_case_info.hpp>
#include <catch2/reporters/catch_reporter_registrars.hpp>
#include <iostream>
class PartialReporter : public Catch::StreamingReporterBase {
public:
using StreamingReporterBase::StreamingReporterBase;
static std::string getDescription() {
return "Reporter for testing TestCasePartialStarting/Ended events";
}
void testCasePartialStarting(Catch::TestCaseInfo const& testInfo,
uint64_t partNumber) override {
std::cout << "TestCaseStartingPartial: " << testInfo.name << '#' << partNumber << '\n';
}
void testCasePartialEnded(Catch::TestCaseStats const& testCaseStats,
uint64_t partNumber) override {
std::cout << "TestCasePartialEnded: " << testCaseStats.testInfo->name << '#' << partNumber << '\n';
}
};
CATCH_REGISTER_REPORTER("partial", PartialReporter)This create a simple reporter that responds to testCasePartial* events,
and calls itself "partial" reporter, so it can be invoked with
--reporter partial command line flag.
Each reporter instance contains instance of ReporterPreferences, a type
that holds flags for the behaviour of Catch2 when this reporter run.
Currently there are two customization options:
shouldRedirectStdOut- whether the reporter wants to handle writes to stdout/stderr from user code, or not. This is useful for reporters that output machine-parseable output, e.g. the JUnit reporter, or the XML reporter.shouldReportAllAssertions- whether the reporter wants to handleassertionEndedevents for passing assertions as well as failing assertions. Usually reporters do not report successful assertions and don't need them for their output, but sometimes the desired output format includes passing assertions even without the-sflag.
Per-reporter configuration was introduced in Catch2 3.0.1
Catch2 supports some configuration to happen per reporter. The configuration options fall into one of two categories:
- Catch2-recognized options
- Reporter-specific options
The former is a small set of universal options that Catch2 handles for
the reporters, e.g. output file or console colour mode. The latter are
options that the reporters have to handle themselves, but the keys and
values can be arbitrary strings, as long as they don't contain ::. This
allows writing reporters that can be significantly customized at runtime.
Reporter-specific options always have to be prefixed with "X" (large letter X).
When writing a custom reporter, there are few more things that you should keep in mind. These are not important for correctness, but they are important for the reporter to work nicely.
-
Catch2 provides a simple verbosity option for users. There are three verbosity levels, "quiet", "normal", and "high", and if it makes sense for reporter's output format, it should respond to these by changing what, and how much, it writes out.
-
Catch2 operates with an rng-seed. Knowing what seed a test run had is important if you want to replicate it, so your reporter should report the rng-seed, if at all possible given the target output format.
-
Catch2 also operates with test filters, or test specs. If a filter is present, you should also report the filter, if at all possible given the target output format.