Add unit tests for errorEntity deserialization feature

- Add JavaJersey3ErrorEntityTest with 8 test cases
- Tests verify template changes for errorEntity feature
- 642 Java tests passed - no regressions
- Fixes #4777

Author: Chhida

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/jersey3/JavaJersey3ErrorEntityTest.java

@@ -0,0 +1,151 @@
+/*
+ * Copyright 2018 OpenAPI-Generator Contributors (https://openapi-generator.tech)
+ * Copyright 2018 SmartBear Software
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.openapitools.codegen.java.jersey3;
+
+import org.testng.annotations.Test;
+import static org.testng.Assert.*;
+
+/**
+ * Tests for error entity deserialization in jersey3 client
+ * 
+ * These tests verify that the templates generate the correct code
+ * for errorEntity feature (issue #4777)
+ */
+public class JavaJersey3ErrorEntityTest {
+
+    private static final String JERSEY3_TEMPLATE_DIR = 
+        "src/main/resources/Java/libraries/jersey3/";
+
+    /**
+     * Test that apiException.mustache contains errorEntity field
+     */
+    @Test
+    public void testApiExceptionHasErrorEntityField() throws Exception {
+        String template = readTemplate("apiException.mustache");
+        assertNotNull(template, "apiException.mustache should exist");
+        assertTrue(template.contains("errorEntity"), 
+            "apiException.mustache should contain 'errorEntity' field");
+    }
+
+    /**
+     * Test that apiException.mustache contains getErrorEntity method
+     */
+    @Test
+    public void testApiExceptionHasGetErrorEntityMethod() throws Exception {
+        String template = readTemplate("apiException.mustache");
+        assertNotNull(template);
+        assertTrue(template.contains("getErrorEntity"), 
+            "apiException.mustache should contain 'getErrorEntity()' method");
+    }
+
+    /**
+     * Test that ApiClient.mustache contains deserializeErrorEntity method
+     */
+    @Test
+    public void testApiClientHasDeserializeErrorEntityMethod() throws Exception {
+        String template = readTemplate("ApiClient.mustache");
+        assertNotNull(template);
+        assertTrue(template.contains("deserializeErrorEntity"), 
+            "ApiClient.mustache should contain 'deserializeErrorEntity' method");
+    }
+
+    /**
+     * Test that api.mustache contains localVarErrorTypes
+     */
+    @Test
+    public void testApiGeneratesErrorTypesMap() throws Exception {
+        String template = readTemplate("api.mustache");
+        assertNotNull(template);
+        assertTrue(template.contains("localVarErrorTypes"), 
+            "api.mustache should contain 'localVarErrorTypes'");
+    }
+
+    /**
+     * Test that invokeAPI accepts errorTypes parameter
+     */
+    @Test
+    public void testInvokeAPIHasErrorTypesParameter() throws Exception {
+        String template = readTemplate("ApiClient.mustache");
+        assertNotNull(template);
+        assertTrue(template.contains("errorTypes"), 
+            "ApiClient.mustache should contain 'errorTypes' parameter");
+    }
+
+    /**
+     * Test that template handles "default" response (uses "0" as key)
+     */
+    @Test
+    public void testDefaultResponseHandling() throws Exception {
+        String template = readTemplate("ApiClient.mustache");
+        assertNotNull(template);
+        assertTrue(template.contains("\"0\""), 
+            "ApiClient.mustache should handle 'default' response with '0' key");
+    }
+
+    /**
+     * Test error types map building pattern
+     */
+    @Test
+    public void testErrorTypesMapBuildingPattern() throws Exception {
+        String template = readTemplate("api.mustache");
+        assertNotNull(template);
+        // Check pattern: localVarErrorTypes.put("code", new GenericType<...>)
+        assertTrue(template.contains("localVarErrorTypes.put"), 
+            "api.mustache should build error types map using put");
+    }
+
+    /**
+     * Test backward compatibility - null is passed for errorTypes
+     */
+    @Test
+    public void testBackwardCompatibility() throws Exception {
+        String template = readTemplate("ApiClient.mustache");
+        assertNotNull(template);
+        // Check that null is passed for backward compatibility
+        assertTrue(template.contains(", null") || 
+                   template.contains("null,") ||
+                   template.contains("null/*"),
+            "Backwards compatibility: null should be passed for errorTypes");
+    }
+
+    /**
+     * Helper method to read template files
+     */
+    private String readTemplate(String templateName) throws Exception {
+        java.nio.file.Path templatePath = java.nio.file.Paths.get(
+            JERSEY3_TEMPLATE_DIR + templateName);
+        if (!java.nio.file.Files.exists(templatePath)) {
+            // Try alternate path
+            templatePath = java.nio.file.Paths.get(
+                "modules/openapi-generator/" + JERSEY3_TEMPLATE_DIR + templateName);
+        }
+        if (java.nio.file.Files.exists(templatePath)) {
+            return java.nio.file.Files.readString(templatePath);
+        }
+        // Try classpath
+        try {
+            java.io.InputStream is = getClass().getClassLoader()
+                .getResourceAsStream(JERSEY3_TEMPLATE_DIR + templateName);
+            if (is != null) {
+                return new String(is.readAllBytes());
+            }
+        } catch (Exception ignored) {}
+        
+        return null;
+    }
+}