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Testing Core Type Adapter Overrides in Google Gson

This test suite validates the functionality of overriding core type adapters in the Gson library, focusing on custom serialization and deserialization of primitive types and strings. The tests demonstrate how to customize JSON conversion behavior for boolean and string values.

Test Coverage Overview

The test suite provides comprehensive coverage of core type adapter overrides in Gson.

Key areas tested include:

Boolean primitive and wrapper type adaptation
Custom string value transformation
Integration with GsonBuilder configuration
Serialization and deserialization with custom type adapters

Implementation Analysis

The testing approach uses JUnit to verify custom TypeAdapter implementations for core Java types. The tests implement two main adapter patterns:

Boolean to integer conversion (0/1 instead of true/false)
String case transformation (uppercase for writing, lowercase for reading)

Each adapter is tested for both serialization and deserialization scenarios.

Technical Details

Testing tools and configuration:

JUnit test framework
Google Truth assertion library
Custom TypeAdapter implementations
GsonBuilder for adapter registration
JsonReader and JsonWriter for low-level JSON handling

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test methods for each adapter type
Comprehensive verification of both primitive and wrapper types
Clear test method naming conventions
Thorough assertion coverage for both serialization and deserialization
Proper setup of test dependencies and configurations

google/gson

gson/src/test/java/com/google/gson/OverrideCoreTypeAdaptersTest.java

            
/*
 * Copyright (C) 2012 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;

import static com.google.common.truth.Truth.assertThat;

import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.util.Locale;
import org.junit.Test;

/**
 * Tests handling of Core Type Adapters
 *
 * @author Jesse Wilson
 */
public class OverrideCoreTypeAdaptersTest {
  private static final TypeAdapter<Boolean> booleanAsIntAdapter =
      new TypeAdapter<>() {
        @Override
        public void write(JsonWriter out, Boolean value) throws IOException {
          out.value(value ? 1 : 0);
        }

        @Override
        public Boolean read(JsonReader in) throws IOException {
          int value = in.nextInt();
          return value != 0;
        }
      };

  private static final TypeAdapter<String> swapCaseStringAdapter =
      new TypeAdapter<>() {
        @Override
        public void write(JsonWriter out, String value) throws IOException {
          out.value(value.toUpperCase(Locale.US));
        }

        @Override
        public String read(JsonReader in) throws IOException {
          return in.nextString().toLowerCase(Locale.US);
        }
      };

  @Test
  public void testOverrideWrapperBooleanAdapter() {
    Gson gson = new GsonBuilder().registerTypeAdapter(Boolean.class, booleanAsIntAdapter).create();
    assertThat(gson.toJson(true, boolean.class)).isEqualTo("true");
    assertThat(gson.toJson(true, Boolean.class)).isEqualTo("1");
    assertThat(gson.fromJson("true", boolean.class)).isEqualTo(Boolean.TRUE);
    assertThat(gson.fromJson("1", Boolean.class)).isEqualTo(Boolean.TRUE);
    assertThat(gson.fromJson("0", Boolean.class)).isEqualTo(Boolean.FALSE);
  }

  @Test
  public void testOverridePrimitiveBooleanAdapter() {
    Gson gson = new GsonBuilder().registerTypeAdapter(boolean.class, booleanAsIntAdapter).create();
    assertThat(gson.toJson(true, boolean.class)).isEqualTo("1");
    assertThat(gson.toJson(true, Boolean.class)).isEqualTo("true");
    assertThat(gson.fromJson("1", boolean.class)).isEqualTo(Boolean.TRUE);
    assertThat(gson.fromJson("true", Boolean.class)).isEqualTo(Boolean.TRUE);
    assertThat(gson.toJson(false, boolean.class)).isEqualTo("0");
  }

  @Test
  public void testOverrideStringAdapter() {
    Gson gson = new GsonBuilder().registerTypeAdapter(String.class, swapCaseStringAdapter).create();
    assertThat(gson.toJson("Hello", String.class)).isEqualTo("\"HELLO\"");
    assertThat(gson.fromJson("\"Hello\"", String.class)).isEqualTo("hello");
  }
}