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Testing JPMS Reflection Accessibility Controls in google/gson

This test suite validates Gson’s behavior when attempting to use reflection on classes in packages that haven’t been explicitly opened to the Gson module. It ensures proper handling of reflection accessibility restrictions in Java Platform Module System (JPMS) contexts.

Test Coverage Overview

The test suite provides comprehensive coverage of reflection accessibility constraints in JPMS environments. It specifically tests:

Deserialization attempts on inaccessible fields
Serialization attempts on inaccessible fields
Proper error message generation with troubleshooting links
Module-level access control validation

Implementation Analysis

The testing approach utilizes JUnit to verify Gson’s behavior when encountering reflection restrictions. It implements two key test cases that verify both serialization and deserialization scenarios, using a private static test class with an inaccessible field. The tests expect specific JsonIOException responses with detailed error messages.

Technical Details

Testing tools and configuration include:

JUnit test framework for test execution
Google Truth assertion library for enhanced assertion capabilities
Gson library for JSON processing
Custom static test class with controlled accessibility
JPMS module configuration tests

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Precise exception message validation
Separate test methods for distinct operations
Clear test method naming conventions
Proper use of assertion frameworks
Comprehensive error message verification
Documentation of expected behavior

google/gson

test-jpms/src/test/java/com/google/gson/jpms_test/ReflectionInaccessibleTest.java

            
/*
 * Copyright (C) 2024 Google Inc.
 *
 * 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
 *
 *      http://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 com.google.gson.jpms_test;

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.assertThrows;

import com.google.gson.Gson;
import com.google.gson.JsonIOException;
import org.junit.Test;

/**
 * Verifies that Gson cannot use reflection for classes in a package if it has not been 'opened' to
 * the Gson module in the {@code module-info.java} of the project.
 */
public class ReflectionInaccessibleTest {
  private static class MyClass {
    @SuppressWarnings("unused")
    int i;
  }

  @Test
  public void testDeserialization() {
    Gson gson = new Gson();
    var e = assertThrows(JsonIOException.class, () -> gson.fromJson("{\"i\":1}", MyClass.class));
    assertThat(e)
        .hasMessageThat()
        .isEqualTo(
            "Failed making field '"
                + MyClass.class.getName()
                + "#i' accessible; either increase its visibility or write a custom TypeAdapter for"
                + " its declaring type.\n"
                + "See https://github.com/google/gson/blob/main/Troubleshooting.md#reflection-inaccessible-to-module-gson");
  }

  @Test
  public void testSerialization() {
    Gson gson = new Gson();

    MyClass obj = new MyClass();
    obj.i = 1;
    var e = assertThrows(JsonIOException.class, () -> gson.toJson(obj));
    assertThat(e)
        .hasMessageThat()
        .isEqualTo(
            "Failed making field '"
                + MyClass.class.getName()
                + "#i' accessible; either increase its visibility or write a custom TypeAdapter for"
                + " its declaring type.\n"
                + "See https://github.com/google/gson/blob/main/Troubleshooting.md#reflection-inaccessible-to-module-gson");
  }
}