Document gitlab integration. (#7)

Author: reznikmm

README.md

@@ -11,6 +11,7 @@ Minimum Effort Ada Unit Testing Library
 - Parallelization of tests
 - Randomization of test order to find dependencies between tests
 - No generated code or scripts needed
+- [JUnit XML reports and GitLab integration](docs/gitlab.md)
 
 ## Example
 

docs/gitlab-pipeline.png

@@ -0,0 +1,92 @@
+# GitLab integration
+
+Gitlab CI can import test information using XML format.
+Here's how to do it. For example, let's create a primitive library
+and tests for it on trendy_test:
+
+```shell
+alr init --in-place --lib test2
+cd test2
+alr init --bin testsuite
+cd testsuite
+alr with test2 --use=..
+alr with trendy_test --use=https://github.com/pyjarrett/trendy_test
+```
+
+Let's add a simple function that we will test later:
+```ada
+package Test2 is
+
+   function Inc (Value : Integer) return Integer is
+     (Value + 1);
+
+end Test2;
+```
+
+The simplest test might look like this:
+```ada
+with Test2;
+
+with Trendy_Test;
+with Trendy_Test.XML_Reports;
+
+procedure Testsuite is
+   
+   procedure Test_Inc (T : in out Trendy_Test.Operation'Class) is
+   begin
+      T.Register;  -- Don't put anything above here
+      
+      Trendy_Test.Assert
+        (T, Condition => Test2.Inc (2) = 3);
+   end Test_Inc;
+   
+   My_Tests : constant Trendy_Test.Test_Group :=
+     (1 => Test_Inc'Unrestricted_Access);
+begin
+   Trendy_Test.Register (My_Tests);
+
+   Trendy_Test.XML_Reports.Print_XML_Report
+     (File_Name => "junit.xml",
+      Results   => Trendy_Test.Run);
+end Testsuite;
+```
+
+After running such a test, it leaves an XML report `junit.xml` in the current directory.
+
+Let's create a GitLab CI description file `.gitlab-ci.yml`:
+
+```yaml
+default:
+  image: ubuntu:22.04
+build-job:
+  stage: build
+  script:
+    - ./.ci-script.sh
+
+  artifacts:
+    when: always
+    paths:
+      - testsuite/junit.xml
+    reports:
+      junit: testsuite/junit.xml
+```
+
+And the bash script itself `.ci-script.sh`:
+
+```shell
+#!/bin/sh
+apt-get update -y
+apt-get install -y curl zip git libc6-dev
+curl -L -O https://github.com/alire-project/alire/releases/download/v2.1.0/alr-2.1.0-bin-x86_64-linux.zip
+unzip alr*.zip
+PATH=$PWD/bin:$PATH
+alr toolchain --select gprbuild^25 gnat_native^15
+alr -C testsuite run
+```
+
+Having added all this to the gitlab repository, we will see the tests
+on the **Tests** tab in **Pipelines**:
+
+![GitLab Pipeline screenshot](gitlab-pipeline.png)
+
+Repository with example: [gitlab.com/reznikmm/test2](https://gitlab.com/reznikmm/test2)