Create a basic test for Grasscutter's HTTP server

src/test/java/io/grasscutter/GrasscutterTest.java

@@ -0,0 +1,67 @@
+package io.grasscutter;
+
+import com.mchange.util.AssertException;
+import emu.grasscutter.Grasscutter;
+import emu.grasscutter.config.Configuration;
+import lombok.Getter;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+/**
+ * Testing entrypoint for {@link Grasscutter}.
+ */
+public final class GrasscutterTest {
+    @Getter private static final OkHttpClient httpClient
+        = new OkHttpClient();
+
+    @Getter private static int httpPort = -1;
+    @Getter private static int gamePort = -1;
+
+    /**
+     * Creates an HTTP URL.
+     *
+     * @param route The route to use.
+     * @return The URL.
+     */
+    public static String http(String route) {
+        return "http://127.0.0.1:" + GrasscutterTest.httpPort + "/" + route;
+    }
+
+    @BeforeAll
+    public static void main() {
+        try {
+            // Start Grasscutter.
+            Grasscutter.main(new String[]{"-test"});
+        } catch (Exception ignored) {
+            throw new AssertException("Grasscutter failed to start.");
+        }
+
+        // Set the ports.
+        GrasscutterTest.httpPort = Configuration.SERVER.http.bindPort;
+        GrasscutterTest.gamePort = Configuration.SERVER.game.bindPort;
+    }
+
+    @Test
+    @DisplayName("HTTP server check")
+    public void checkHttpServer() {
+        // Create a request.
+        var request = new Request.Builder()
+            .url(GrasscutterTest.http(""))
+            .build();
+
+        // Perform the request.
+        try (var response = GrasscutterTest.httpClient
+            .newCall(request).execute()) {
+            // Check the response.
+            Assertions.assertTrue(response.isSuccessful());
+        } catch (IOException exception) {
+            throw new AssertionError(exception);
+        }
+    }
+}