[java][resttemplate] Add test to ensure additional properties work

bin/utils/test_file_list.yaml

@@ -15,3 +15,6 @@
   sha256: 8b1b8f2a2ad00ccb090873a94a5f73e328b98317d2ec715f53bd7a1accb2a023
 - filename: "samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/model/PetTest.java"
   sha256: a1f8a70bf7b0c382a8def5bacf7b1fb189e687fabb40235aa799001e0597f545
+# java resttemplate test files
+- filename: "samples/client/petstore/java/resttemplate/src/test/java/org/openapitools/client/JacksonTest.java"
+  sha256: 346af62abe32357474f0da870f75fbc1b765b0efe64eee40ddfc0f0d6fd43a97

samples/client/petstore/java/resttemplate/src/test/java/org/openapitools/client/JacksonTest.java

@@ -0,0 +1,64 @@
+package org.openapitools.client;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.openapitools.client.model.TestInlineFreeformAdditionalPropertiesRequest;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class JacksonTest {
+
+    private ObjectMapper mapper;
+
+    @BeforeEach
+    void setUp() {
+        mapper = JsonMapper.builder()
+            // For determinist serialization results
+            .enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY)
+            .enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS)
+            .build();
+    }
+
+    @Test
+    void testSerializeAdditionalProperties() throws JsonProcessingException {
+        // Given
+        TestInlineFreeformAdditionalPropertiesRequest model = new TestInlineFreeformAdditionalPropertiesRequest("value")
+            .putAdditionalProperty("someString", "someValue")
+            .putAdditionalProperty("someNumber", 1.23)
+            .putAdditionalProperty("someBoolean", true);
+
+        // When
+        String string = mapper.writeValueAsString(model);
+
+        // Then
+        String expectedString = "{\"someProperty\":\"value\",\"someBoolean\":true,\"someNumber\":1.23,\"someString\":\"someValue\"}";
+        assertEquals(expectedString, string);
+    }
+
+    @Test
+    void testDeserializeAdditionalProperties() throws JsonProcessingException {
+        // Given
+        String string = "{\"someProperty\":\"value\",\"someBoolean\":true,\"someNumber\":1.23,\"someString\":\"someValue\"}";
+
+        // When
+        TestInlineFreeformAdditionalPropertiesRequest model = mapper.readValue(
+            string,
+            TestInlineFreeformAdditionalPropertiesRequest.class
+        );
+
+        // Then
+        TestInlineFreeformAdditionalPropertiesRequest expectedModel = new TestInlineFreeformAdditionalPropertiesRequest("value")
+            .putAdditionalProperty("someString", "someValue")
+            .putAdditionalProperty("someNumber", 1.23)
+            .putAdditionalProperty("someBoolean", true);
+        assertEquals(expectedModel, model);
+
+        TestInlineFreeformAdditionalPropertiesRequest invalidModel = new TestInlineFreeformAdditionalPropertiesRequest("value");
+        assertNotEquals(invalidModel, model);
+    }
+}