Add section about operating system specific tests (#7755)

* add section about operating system specific tests

* Update content/doc/developer/testing/index.adoc

Co-authored-by: Zbynek Konecny <[email protected]>

* Apply suggestions from code review

Co-authored-by: Mark Waite <[email protected]>

---------

Co-authored-by: Zbynek Konecny <[email protected]>
Co-authored-by: Mark Waite <[email protected]>

content/doc/developer/testing/index.adoc

@@ -246,6 +246,51 @@ To recreate the same configuration from a test method, you can do the following:
 In order to test parts of your plugin, you may want certain files to exist in the build workspace, or that Jenkins is configured in a certain way.
 This section covers various ways to achieve this using the Jenkins Test Harness.
 
+=== Operating System Awareness
+
+Sometimes it is necessary to adjust a test depending on the operating system.
+This can be the choice of Batch or Shell commands or other test conditions that are operating system specific.
+The following example uses `Functions.isWindows()` to create different code depending on the operating system:
+
+[source,java]
+----
+import hudson.Functions;
+import hudson.model.FreeStyleProject;
+import hudson.tasks.BatchFile;
+import hudson.tasks.Shell;
+import org.jvnet.hudson.test.JenkinsRule;
+import org.junit.Rule;
+import org.junit.Test;
+
+public class MyPluginTest {
+
+    @Rule
+    public JenkinsRule j = new JenkinsRule();
+
+    @Test
+    public void testOnAllSystems() throws Exception {
+        FreeStyleProject project = j.createFreeStyleProject();
+        if (Functions.isWindows()) {
+            project.getBuildersList().add(new BatchFile("echo ahoy > log.log"));
+        } else {
+            project.getBuildersList().add(new Shell("echo ahoy > log.log"));
+        }
+        j.buildAndAssertSuccess(project);
+    }
+}
+----
+
+Sometimes a test should be skipped because it is only relevant for one type of operating system or because it needs specific conditions that depend on the test environment.
+Tests can be skipped based on conditionals evaluated by link:https://www.baeldung.com/junit-conditional-assume[JUnit Assume].
+Use  `assumeFalse()` to disable a test on Windows systems in combination with `Functions.isWindows()`:
+
+`assumeFalse("TODO: Implement this test on Windows", Functions.isWindows());`
+
+The test will be skipped on Windows.
+
+Tests run on all platforms by default.
+Jenkins encourages testing on multiple operating systems, including Windows.
+
 ==== Customizing the Build Workspace