Add tests for gson (#5182)

* Add tests for gson

Signed-off-by: Holger Friedrich <mail@holger-friedrich.de>

bundles/org.openhab.core/src/test/java/org/openhab/core/gson/GsonTest.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.gson;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.junit.jupiter.api.Test;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+/**
+ * Gson deserialization, DTOs.
+ *
+ * @author Holger Friedrich - Initial contribution
+ */
+@NonNullByDefault
+class GsonTest {
+
+    private static final Gson GSON = new GsonBuilder().create();
+
+    /**
+     * Load the test JSON payload string from a file (copied from hue binding)
+     */
+    private String load(String fileName) {
+        try (FileReader file = new FileReader(String.format("src/test/resources/%s.json", fileName));
+                BufferedReader reader = new BufferedReader(file)) {
+            StringBuilder builder = new StringBuilder();
+            String line;
+            while ((line = reader.readLine()) != null) {
+                builder.append(line).append("\n");
+            }
+            return builder.toString();
+        } catch (IOException e) {
+            fail(e.getMessage());
+        }
+        return "";
+    }
+
+    @Test
+    void testLoadAndDeserializeJson() {
+        // Load JSON from file
+        String json = load("testdata");
+        assertNotNull(json, "JSON content should not be null");
+        assertFalse(json.isEmpty(), "JSON content should not be empty");
+
+        // Deserialize into GsonTestClass_DTO
+        GsonTestClass_DTO test = GSON.fromJson(json, GsonTestClass_DTO.class);
+        assertNotNull(test, "Deserialized object should not be null");
+
+        // Verify all fields are correctly deserialized
+        assertEquals("John Doe", test.name, "Name field should match");
+        assertEquals(30, test.age, "Age field should match");
+        assertEquals("john.doe@example.com", test.email, "Email field should match");
+        assertTrue(test.active, "Active field should match");
+    }
+
+    @Test
+    void testLoadAndDeserializeAnnotatedJson() {
+        // Load JSON from file
+        String json = load("testdata");
+        assertNotNull(json, "JSON content should not be null");
+        assertFalse(json.isEmpty(), "JSON content should not be empty");
+
+        // Deserialize into GsonTestClassAnnotated_DTO
+        GsonTestClassAnnotated_DTO test = GSON.fromJson(json, GsonTestClassAnnotated_DTO.class);
+        assertNotNull(test, "Deserialized object should not be null");
+
+        // Verify all fields are correctly deserialized
+        assertEquals("John Doe", test.n, "Name field should match");
+        assertEquals(30, test.age, "Age field should match");
+        assertTrue(test.active, "Active field should match");
+        assertEquals("john.doe@example.com", test.e, "Email field should match");
+    }
+
+    @Test
+    void testLoadAndDeserializeAnnotated2Json() {
+        // Load JSON from file
+        String json = load("testdata");
+        assertNotNull(json, "JSON content should not be null");
+        assertFalse(json.isEmpty(), "JSON content should not be empty");
+
+        // Deserialize into GsonTestClassAnnotated2_DTO
+        GsonTestClassAnnotated2_DTO test = GSON.fromJson(json, GsonTestClassAnnotated2_DTO.class);
+        assertNotNull(test, "Deserialized object should not be null");
+
+        // Verify all fields are correctly deserialized
+        assertEquals("John Doe", test.n, "Name field should match");
+        assertEquals(30, test.age, "Age field should match");
+        assertTrue(test.active, "Active field should match");
+        assertEquals("john.doe@example.com", test.e, "Email field should match");
+    }
+}

bundles/org.openhab.core/src/test/java/org/openhab/core/gson/GsonTestClassAnnotated2_DTO.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.gson;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Example Test for testing Gson deserialization.
+ *
+ * @author Holger Friedrich - Initial contribution
+ */
+@NonNullByDefault
+public class GsonTestClassAnnotated2_DTO {
+    public @SerializedName("name") @Nullable String n;
+    public @Nullable @SerializedName("email") String e;
+    public int age;
+    public boolean active;
+
+    public GsonTestClassAnnotated2_DTO() {
+    }
+
+    public GsonTestClassAnnotated2_DTO(String name, int age, String email, boolean active) {
+        this.n = name;
+        this.e = email;
+        this.age = age;
+        this.active = active;
+    }
+
+    @Override
+    public String toString() {
+        return "GsonTestClassAnnotated2_DTO{" + "name='" + n + '\'' + ", age=" + age + ", email='" + e + '\''
+                + ", active=" + active + '}';
+    }
+}

bundles/org.openhab.core/src/test/java/org/openhab/core/gson/GsonTestClassAnnotated_DTO.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.gson;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+
+import com.google.gson.annotations.SerializedName;
+
+/**
+ * Example Test for testing Gson deserialization.
+ *
+ * @author Holger Friedrich - Initial contribution
+ */
+@NonNullByDefault
+public class GsonTestClassAnnotated_DTO {
+    // adding annotations in different order is intended, please do not sort!
+    public @SerializedName("name") @NonNullByDefault({}) String n = null;
+    public @NonNullByDefault({}) @SerializedName("email") String e = null;
+    public int age;
+    public boolean active;
+
+    public GsonTestClassAnnotated_DTO() {
+    }
+
+    public GsonTestClassAnnotated_DTO(String name, int age, String email, boolean active) {
+        this.n = name;
+        this.e = email;
+        this.age = age;
+        this.active = active;
+    }
+
+    @Override
+    public String toString() {
+        return "GsonTestClassAnnotated_DTO{" + "name='" + n + '\'' + ", age=" + age + ", email='" + e + '\''
+                + ", active=" + active + '}';
+    }
+}

bundles/org.openhab.core/src/test/java/org/openhab/core/gson/GsonTestClass_DTO.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2010-2025 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.gson;
+
+/**
+ * Example Test for testing Gson deserialization.
+ *
+ * @author Holger Friedrich - Initial contribution
+ */
+public class GsonTestClass_DTO {
+    public String name;
+    public int age;
+    public String email;
+    public boolean active;
+
+    public GsonTestClass_DTO() {
+    }
+
+    public GsonTestClass_DTO(String name, int age, String email, boolean active) {
+        this.name = name;
+        this.age = age;
+        this.email = email;
+        this.active = active;
+    }
+
+    @Override
+    public String toString() {
+        return "GsonTestClass{" + "name='" + name + '\'' + ", age=" + age + ", email='" + email + '\'' + ", active="
+                + active + '}';
+    }
+}

bundles/org.openhab.core/src/test/resources/testdata.json

@@ -0,0 +1,6 @@
+{
+  "name": "John Doe",
+  "age": 30,
+  "email": "john.doe@example.com",
+  "active": true
+}