TestRail extension which reports test run results to TestRail and creates a basic test run which is not part of any test plan.

TestRailReportExtension.java

public class TestRailReportExtension implements TestWatcher, BeforeAllCallback {

    private static boolean started = false;
    private static final String TESTRAIL_REPORT = "TEST_RAIL";
    private static List<Result> results = new CopyOnWriteArrayList<>();


    @Override
    public void testDisabled(ExtensionContext extensionContext, Optional<String> optional) {
        addResult(extensionContext, TestRailStatus.DISABLED);
    }

    @Override
    public void testSuccessful(ExtensionContext extensionContext) {
        addResult(extensionContext, TestRailStatus.PASSED);
    }

    @Override
    public void testAborted(ExtensionContext extensionContext, Throwable throwable) {
        addResult(extensionContext, TestRailStatus.RETEST);
    }

    @Override
    public void testFailed(ExtensionContext extensionContext, Throwable throwable) {
        addResult(extensionContext, TestRailStatus.FAILED);
    }

    @Override
    public void beforeAll(ExtensionContext extensionContext) {
        if (!started) {
            getStore(extensionContext).put(TESTRAIL_REPORT, new CloseableOnlyOnceResource());
            started = true;
        }

    }

    private static class CloseableOnlyOnceResource implements
            ExtensionContext.Store.CloseableResource {
        @Override
        public void close() {
            //After all tests run hook.
            //Any additional desired action goes here
            reportResults();
        }
    }

    private void addResult(ExtensionContext extensionContext, TestRailStatus status) {
        //TmsLink is an annotation from Allure framework
        if (extensionContext.getElement().isPresent() && extensionContext.getElement().get().isAnnotationPresent(
                TmsLink.class)) {
            TmsLink element = extensionContext.getElement().get().getAnnotation(TmsLink.class);
            String exceptionMessage = extensionContext.getExecutionException().map(Throwable::getMessage).orElse(null);
            Result result = new Result().setComment(exceptionMessage).setTestId(Integer.parseInt(element.value())).setStatusId(status.getId())
                    .setCaseId(Integer.valueOf(element.value()));
            addResult(result);
        }
    }

    private ExtensionContext.Store getStore(ExtensionContext context) {
        return context.getRoot().getStore(ExtensionContext.Namespace.GLOBAL);
    }

    private static void addResult(Result result) {
        results.add(result);
    }

    private static void reportResults() {
        if (testRailEnabled()) { // replace with your own method of reading data from prom properties file 
            final String url = "http://testrail.example.com";
            final String userId = "email@example.com";
            final String pwd = "1q2w3e";
            final Integer projectId = "18";
            final Integer testSuiteId = 1234; // Suite ID should be unique per project
            final Integer planId = 1111; // Test plan reflects current version which is tested
            final Integer milestone = 666; // Milestone is set per each project and should reflect release version(e.g. 1.0, 666)
            final String browserName = "browserName";
            final String description = "Test Run description. It can contain links to build or some other useful information";
            final String name = "Test run name";
            TestRail testRail = TestRail.builder(url, userId, pwd).build();

            Project project = testRail.projects().get(projectId).execute();
            Run run = testRail.runs()
                    .add(project.getId(),
                            new Run().setName(name)
                                    .setDescription(description)
                                    .setIncludeAll(false)
                                    .setSuiteId(testSuiteId)
                                    .setMilestoneId(milestone)
                                    .setPlanId(planId)
                                    .setCaseIds(results.stream()
                                            .map(Result::getCaseId).collect(Collectors.toCollection(CopyOnWriteArrayList::new)))
                    ).execute();
            List<ResultField> customResultFields = testRail.resultFields().list().execute();
            List<CaseField> caseFields = testRail.caseFields().list().execute();
            List<Result> finalResults;
            finalResults = results;
            for (Result result : results) {
                try {
                    testRail.cases().get(result.getCaseId(), caseFields).execute();
                } catch (Exception e) {
                    finalResults.remove(result);
                    System.out.println("Test Case with ID " + result.getCaseId() + " does not exist in TestRail! \n");
                }
            }
            testRail.results().addForCases(run.getId(), finalResults, customResultFields).execute();
            testRail.runs().close(run.getId()).execute();
        } else System.out.println("TestRail reporting is disabled... Skipping");
    }

    private enum TestRailStatus {
        PASSED(1),
        BLOCKED(2),
        UNTESTED(3),
        RETEST(4),
        FAILED(5),
        DISABLED(6); //This is a custom test status added manually!

        private int id;

        public int getId() {
            return id;
        }

        TestRailStatus(int id) {
            this.id = id;
        }
    }