feat: add reference implementation

Author: vitorsalgado

build.gradle

@@ -1,4 +1,5 @@
 plugins {
+    id 'idea'
     id 'java'
 }
 
@@ -10,7 +11,10 @@ repositories {
 }
 
 dependencies {
-    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.2'
+    implementation 'org.junit.jupiter:junit-jupiter-api:5.7.2'
+    implementation 'com.fasterxml.jackson.core:jackson-core:2.12.5'
+    implementation 'com.fasterxml.jackson.core:jackson-databind:2.12.5'
+
     testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.2'
 }
 

src/main/java/org/example/Fixture.java

@@ -0,0 +1,13 @@
+package org.example;
+
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.PARAMETER)
+public @interface Fixture {
+  String value();
+}

src/main/java/org/example/FixtureParameterResolver.java

@@ -0,0 +1,68 @@
+package org.example;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.junit.jupiter.api.extension.ParameterContext;
+import org.junit.jupiter.api.extension.ParameterResolutionException;
+import org.junit.jupiter.api.extension.ParameterResolver;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+
+public class FixtureParameterResolver implements ParameterResolver {
+
+  public static final String BASE_PATH = "/fixtures/%s";
+  private static final ObjectMapper objectMapper = new ObjectMapper();
+
+  @Override
+  public boolean supportsParameter(final ParameterContext parameterContext, final ExtensionContext extensionContext)
+      throws ParameterResolutionException {
+    return parameterContext.getParameter().isAnnotationPresent(Fixture.class);
+  }
+
+  @Override
+  public Object resolveParameter(final ParameterContext parameterContext, final ExtensionContext extensionContext)
+      throws ParameterResolutionException {
+    Fixture fixture = parameterContext.getParameter().getAnnotation(Fixture.class);
+
+    final String fileName = fixture.value();
+    final String filePath = String.format(BASE_PATH, fileName);
+    final InputStream inputStream = FixtureParameterResolver.class.getResourceAsStream(filePath);
+
+    final String data;
+
+    try {
+      data = readFromInputStream(inputStream);
+    } catch (IOException ex) {
+      throw new ParameterResolutionException(ex.getMessage(), ex);
+    }
+
+    if (parameterContext.getParameter().getType().isAssignableFrom(String.class)) {
+      return data.trim();
+    }
+
+    try {
+      return objectMapper.readValue(data, parameterContext.getParameter().getType());
+    } catch (JsonProcessingException e) {
+      throw new ParameterResolutionException(e.getMessage(), e);
+    }
+  }
+
+  private String readFromInputStream(final InputStream inputStream)
+      throws IOException {
+    final StringBuilder resultStringBuilder = new StringBuilder();
+
+    try (final BufferedReader br
+             = new BufferedReader(new InputStreamReader(inputStream))) {
+      String line;
+      while ((line = br.readLine()) != null) {
+        resultStringBuilder.append(line).append("\n");
+      }
+    }
+
+    return resultStringBuilder.toString();
+  }
+}

src/test/java/org/example/FixtureParameterResolverTest.java

@@ -0,0 +1,45 @@
+package org.example;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+@ExtendWith(FixtureParameterResolver.class)
+public class FixtureParameterResolverTest {
+
+  @Test
+  void test_fixture_annotation_when_fixtureTypeIsObject(final @Fixture("fixtureTest.json") TestData testData) {
+    assertEquals(123, testData.getId());
+    assertEquals("hello world", testData.getTest());
+  }
+
+  @Test
+  void should_return_helloWorldMessage(final @Fixture("fixtureTest.json") String message) {
+    assertEquals("{\n" +
+        "  \"id\": 123,\n" +
+        "  \"test\": \"hello world\"\n" +
+        "}", message);
+  }
+
+  static class TestData {
+    private int id;
+    private String test;
+
+    public TestData(int id, String test) {
+      this.id = id;
+      this.test = test;
+    }
+
+    public TestData() {
+    }
+
+    public int getId() {
+      return id;
+    }
+
+    public String getTest() {
+      return test;
+    }
+  }
+}

src/test/resources/fixtures/fixtureTest.json

@@ -0,0 +1,4 @@
+{
+  "id": 123,
+  "test": "hello world"
+}