reporters

    ## Reporters

    Doctest has a modular reporter/listener system with which users can write their own reporters and register them. The reporter interface can also be used for "listening" to events.

    You can list all registered reporters/listeners with ```--list-reporters```. There are a few implemented reporters in the framework:
    - ```console``` - streaming - writes normal lines of text with coloring if a capable terminal is detected
    - ```xml``` - streaming - writes in xml format tailored to doctest
    - ```junit``` - buffering - writes in JUnit-compatible xml - for more information look [here](https://github.com/doctest/doctest/issues/318) and [here](https://github.com/doctest/doctest/issues/376).

    Streaming means that results are delivered progressively and not at the end of the test run.

    The output is by default written to ```stdout``` but can be redirected with the use of the ```--out=<filename>``` [**command line option**](commandline.html).

    Example how to define your own reporter:

    ```
    #include <doctest/doctest.h>

    #include <mutex>

    using namespace doctest;

    struct MyXmlReporter : public IReporter
    {
        // caching pointers/references to objects of these types - safe to do
        std::ostream&         stdout_stream;
        const ContextOptions& opt;
        const TestCaseData*   tc;
        std::mutex            mutex;

        // constructor has to accept the ContextOptions by ref as a single argument
        MyXmlReporter(const ContextOptions& in)
                : stdout_stream(*in.cout)
                , opt(in) {}

        void report_query(const QueryData& /*in*/) override {}

        void test_run_start() override {}

        void test_run_end(const TestRunStats& /*in*/) override {}

        void test_case_start(const TestCaseData& in) override { tc = &in; }

        // called when a test case is reentered because of unfinished subcases
        void test_case_reenter(const TestCaseData& /*in*/) override {}

        void test_case_end(const CurrentTestCaseStats& /*in*/) override {}

        void test_case_exception(const TestCaseException& /*in*/) override {}

        void subcase_start(const SubcaseSignature& /*in*/) override {
            std::lock_guard<std::mutex> lock(mutex);
        }

        void subcase_end() override {
            std::lock_guard<std::mutex> lock(mutex);
        }

        void log_assert(const AssertData& in) override {
            // don't include successful asserts by default - this is done here
            // instead of in the framework itself because doctest doesn't know
            // if/when a reporter/listener cares about successful results
            if(!in.m_failed && !opt.success)
                return;

            // make sure there are no races - this is done here instead of in the
            // framework itself because doctest doesn't know if reporters/listeners
            // care about successful asserts and thus doesn't lock a mutex unnecessarily
            std::lock_guard<std::mutex> lock(mutex);

            // ...
        }

        void log_message(const MessageData& /*in*/) override {
            // messages too can be used in a multi-threaded context - like asserts
            std::lock_guard<std::mutex> lock(mutex);

            // ...
        }

        void test_case_skipped(const TestCaseData& /*in*/) override {}
    };

    // "1" is the priority - used for ordering when multiple reporters are used
    REGISTER_REPORTER("my_xml", 1, MyXmlReporter);

    // registering the same class as a reporter and as a listener is nonsense but it's possible
    REGISTER_LISTENER("my_listener", 1, MyXmlReporter);
    ```

    Custom `IReporter` implementations must be registered with one of:

    * `REGISTER_REPORTER`, for when the new reporter is an option that users may choose at run-time.
    * `REGISTER_LISTENER`, for when the reporter is actually a listener and must always be executed, regardless of which reporters have been chosen at run-time.

    Multiple reporters can be used at the same time - just specify them through the ```--reporters=...``` [**command line filtering option**](commandline.html) using commas to separate them like this: ```--reporters=myReporter,xml``` and their order of execution will be based on their priority - that is the number "1" in the case of the example reporter above (lower means earlier - the default console/xml reporters from the framework have 0 as their priority and negative numbers are accepted as well).

    All registered listeners (```REGISTER_LISTENER```) will be executed before any reporter - they do not need to be specified and cannot be filtered through the command line.

    When implementing a reporter users are advised to follow the comments from the example above and look at the few implemented reporters in the framework itself. Also check out the [**example**](../../examples/all_features/reporters_and_listeners.cpp).

    ---------------

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