Add example configuration for springdoc-openapi-gradle-plugin to springwolf-kafka-example

- Use springdoc-openapi-gradle-plugin to generate the api spec before test execution 
- Add a test to ensure that the plugin still works for springwolf (#134)

Author: sam0r040

springwolf-examples/springwolf-kafka-example/build.gradle

@@ -5,6 +5,7 @@ plugins {
     id 'io.spring.dependency-management' version '1.1.0'
 
     id 'com.bmuschko.docker-spring-boot-application' version '6.7.0'
+    id 'org.springdoc.openapi-gradle-plugin' version '1.6.0'
 }
 
 sourceCompatibility = '1.8'
@@ -67,3 +68,13 @@ test {
         exceptionFormat = 'full'
     }
 }
+
+openApi {
+    apiDocsUrl = "http://localhost:8080/springwolf/docs"
+    // For testing purposes we put the generated json into the test resources, but it could be any other directory
+    outputDir = file("$buildDir/resources/test")
+    outputFileName = "openapi-generated.json"
+}
+
+// generate the open api docs before tests are executed so that if it works, the json is already there
+test.dependsOn("generateOpenApiDocs")

springwolf-examples/springwolf-kafka-example/src/test/java/io/github/stavshamir/springwolf/example/OpenApiGeneratorTest.java

@@ -0,0 +1,36 @@
+package io.github.stavshamir.springwolf.example;
+
+import org.json.JSONException;
+import org.junit.jupiter.api.Test;
+import org.skyscreamer.jsonassert.JSONAssert;
+import org.skyscreamer.jsonassert.JSONCompareMode;
+import org.testcontainers.shaded.org.apache.commons.io.IOUtils;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * This test is strongly coupled with the configuration of the springdoc openapi plugin in build.gradle
+ * <p>
+ * The gradle project is configured to run the generateOpenApiDocs task before the test task.
+ * The generateOpenApiDocs task will generate the openapi-generated.json into the test-resources so that
+ * this test can pick up the openapi-generated.json afterwards and compare it to the reference asyncapi.json
+ */
+public class OpenApiGeneratorTest {
+
+    @Test
+    public void asyncApiResourceArtifactTest() throws JSONException, IOException {
+
+        InputStream expectedStream  = this.getClass().getResourceAsStream("/asyncapi.json");
+
+        // When running with EmbeddedKafka, localhost is used as hostname
+        String expectedWithoutServersKafkaUrlPatch = IOUtils.toString(expectedStream, StandardCharsets.UTF_8);
+        String expected = expectedWithoutServersKafkaUrlPatch.replace("kafka:29092", "localhost:29092");
+
+        InputStream actualStream = this.getClass().getResourceAsStream("/openapi-generated.json");
+        String actual = IOUtils.toString(actualStream, StandardCharsets.UTF_8);
+
+        JSONAssert.assertEquals(expected, actual, JSONCompareMode.STRICT_ORDER);
+    }
+}