Add basic test and JUnit dependency

.gitignore

@@ -25,3 +25,6 @@ replay_pid*
 
 # Ignore Gradle build output directory
 build
+
+# Ignore vscode settings
+.vscode

build.gradle

@@ -15,11 +15,18 @@ plugins {
 }
 
 repositories {
+  // Snapshot repository for JSpecify conformance test framework
+  maven { url 'https://s01.oss.sonatype.org/content/repositories/snapshots'}
+  maven { url 'https://oss.sonatype.org/content/repositories/snapshots/'}
   mavenCentral()
 }
 
-sourceCompatibility = 1.8
-targetCompatibility = 1.8
+sourceCompatibility = 1.9
+targetCompatibility = 1.9
+
+configurations {
+  jSpecifyConformanceTests
+}
 
 dependencies {
   // Use JUnit Jupiter for testing.
@@ -28,6 +35,9 @@ dependencies {
 
   // This dependency is used by the application.
   implementation 'com.google.guava:guava:31.1-jre'
+
+  testImplementation 'org.jspecify.conformance:conformance-test-framework:0.0.0-SNAPSHOT'
+  jSpecifyConformanceTests 'org.jspecify.conformance:conformance-tests:0.0.0-SNAPSHOT'
 }
 
 spotless {
@@ -53,4 +63,8 @@ spotless {
   }
 }
 
+test {
+  useJUnitPlatform()
+}
+
 mainClassName = 'hello.HelloWorld'

src/test/java/conformance/HelloWorldTest.java

@@ -0,0 +1,12 @@
+package conformance;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class HelloWorldTest {
+  @Test
+  public void testHelloWorld() {
+    assertEquals("Hello, World!", "Hello, World!");
+  }
+}