Add a basic test suite

This puts the infrastructure in place
for adding more tests in the future.

build.gradle

@@ -1,5 +1,6 @@
 plugins {
   id 'application'
+  id 'jvm-test-suite'
   id 'com.diffplug.spotless' version '6.23.3'
   id 'net.ltgt.errorprone' version '3.1.0'
 }
@@ -97,6 +98,35 @@ application {
     '--enable-preview', '--enable-native-access', 'ALL-UNNAMED']
 }
 
+testing {
+  suites {
+    configureEach {
+      dependencies {
+        implementation project()
+        // https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api
+        implementation 'org.junit.jupiter:junit-jupiter-api:5.10.1'
+        runtimeOnly 'org.junit.platform:junit-platform-launcher'
+      }
+    }
+    test(JvmTestSuite) {
+      useJUnitJupiter()
+      testType = TestSuiteType.INTEGRATION_TEST
+    }
+  }
+}
+
+test {
+  reports {
+    junitXml {
+      outputPerTestCase = true
+      mergeReruns = true
+    }
+  }
+  testLogging {
+    events "failed", "passed", "skipped"
+  }
+}
+
 tasks.withType(JavaCompile).configureEach {
   // ErrorProne is slow, only enable with ./gradlew build -Perrorprone.
   options.errorprone.enabled = project.hasProperty('errorprone')

java/org/contikios/cooja/Main.java

@@ -58,7 +58,7 @@
         "Cooja " + Cooja.VERSION + ", Contiki-NG build interface version " + Cooja.CONTIKI_NG_BUILD_VERSION,
         "JVM: ${java.version} (${java.vendor} ${java.vm.name} ${java.vm.version})",
         "OS: ${os.name} ${os.version} ${os.arch}"}, sortOptions = false, sortSynopsis = false)
-class Main {
+public class Main {
   /**
    * Option for specifying look and feel.
    */

src/test/java/TestCooja.java

@@ -0,0 +1,38 @@
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import org.contikios.cooja.Cooja;
+import org.contikios.cooja.Main;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class TestCooja {
+  private final PrintStream stdout = System.out;
+  private final PrintStream stderr = System.err;
+  private final ByteArrayOutputStream out = new ByteArrayOutputStream();
+  private final ByteArrayOutputStream err = new ByteArrayOutputStream();
+
+  @BeforeEach
+  public void setUpStreams() {
+    out.reset();
+    err.reset();
+    System.setOut(new PrintStream(out));
+    System.setErr(new PrintStream(err));
+  }
+
+  @AfterEach
+  public void restoreStreams() {
+    System.setOut(stdout);
+    System.setErr(stderr);
+  }
+
+  @Test
+  void testVersion() {
+    Main.main(new String[] {"--version"});
+    assertEquals("", err.toString());
+    assertTrue(out.toString().contains(Cooja.VERSION));
+  }
+}