Add GraphQlClient and GraphQlTester Kotlin extensions

This commit adds Kotlin extensions for `GraphQlClient` and
`GraphQlTester`. Developers can now use dedicated inline functions with
reified generics instead of using `Class<?>` or
`ParameterizedTypeReference` arguments for expressing the expected
return type.

Closes gh-1331

Author: bclozel

platform/build.gradle

@@ -44,6 +44,7 @@ dependencies {
 		api("org.awaitility:awaitility:4.3.0")
 		api("com.squareup.okhttp3:mockwebserver3:5.1.0")
 		api("org.hamcrest:hamcrest:3.0")
+		api("io.mockk:mockk:1.14.5")
 
 		api("com.h2database:h2:2.3.232")
 		api("org.hibernate.orm:hibernate-core:7.1.0.Final")

spring-graphql-test/build.gradle

@@ -1,5 +1,7 @@
 description = "Spring Support for Testing GraphQL Applications"
 
+apply plugin: "kotlin"
+
 dependencies {
 	api project(':spring-graphql')
 	api 'com.graphql-java:graphql-java'
@@ -27,6 +29,7 @@ dependencies {
 	testImplementation 'org.junit.jupiter:junit-jupiter'
 	testImplementation 'org.assertj:assertj-core'
 	testImplementation 'org.mockito:mockito-core'
+	testImplementation 'io.mockk:mockk'
 	testImplementation 'org.skyscreamer:jsonassert'
 	testImplementation 'org.springframework:spring-messaging'
 	testImplementation 'org.springframework:spring-webflux'

spring-graphql-test/src/main/kotlin/org/springframework/graphql/test/tester/GraphQlTesterExtensions.kt

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * 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.springframework.graphql.test.tester
+
+import org.springframework.core.ParameterizedTypeReference
+
+/**
+ * Extension for [GraphQlTester.Path.entity] providing a `entity<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlTester.Path.entity(): GraphQlTester.Entity<T, *> =
+    entity(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlTester.Path.entityList] providing a `entityList<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlTester.Path.entityList(): GraphQlTester.EntityList<T> =
+    entityList(object : ParameterizedTypeReference<T>() {})

spring-graphql-test/src/test/kotlin/org/springframework/graphql/test/tester/GraphQlTesterExtensionsTests.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * 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.springframework.graphql.test.tester
+
+import io.mockk.mockk
+import io.mockk.verify
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+
+/**
+ * Tests for [GraphQlTester] Kotlin extensions.
+ *
+ * @author Brian Clozel
+ */
+class GraphQlTesterExtensionsTests {
+
+    private val testerPath = mockk<GraphQlTester.Path>(relaxed = true)
+
+    @Test
+    fun `Path#entity with reified type parameters`() {
+        testerPath.entity<Map<String, Book>>()
+        verify { testerPath.entity(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    @Test
+    fun `Path#entityList with reified type parameters`() {
+        testerPath.entityList<Map<String, Book>>()
+        verify { testerPath.entityList(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    private class Book {}
+
+}

spring-graphql/build.gradle

@@ -57,6 +57,7 @@ dependencies {
 	testImplementation 'org.junit.jupiter:junit-jupiter'
 	testImplementation 'org.assertj:assertj-core'
 	testImplementation 'org.mockito:mockito-core'
+	testImplementation 'io.mockk:mockk'
 	testImplementation 'org.awaitility:awaitility'
 	testImplementation 'io.projectreactor:reactor-test'
 	testImplementation "org.jetbrains.kotlin:kotlin-reflect"

spring-graphql/src/main/kotlin/org/springframework/graphql/client/GraphQlClientExtensions.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * 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.springframework.graphql.client
+
+import org.springframework.core.ParameterizedTypeReference
+import reactor.core.publisher.Flux
+import reactor.core.publisher.Mono
+
+/**
+ * Extension for [GraphQlClient.RetrieveSpec.toEntity] providing a `toEntity<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSpec.toEntity(): Mono<T> =
+    toEntity(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlClient.RetrieveSpec.toEntityList] providing a `toEntityList<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSpec.toEntityList(): Mono<List<T>> =
+    toEntityList(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlClient.RetrieveSyncSpec.toEntity] providing a `toEntity<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSyncSpec.toEntity(): T? =
+    toEntity(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlClient.RetrieveSyncSpec.toEntityList] providing a `toEntityList<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSyncSpec.toEntityList(): List<T> =
+    toEntityList(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlClient.RetrieveSubscriptionSpec.toEntity] providing a `toEntity<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSubscriptionSpec.toEntity(): Flux<T> =
+    toEntity(object : ParameterizedTypeReference<T>() {})
+
+/**
+ * Extension for [GraphQlClient.RetrieveSubscriptionSpec.toEntityList] providing a `toEntityList<Book>()` variant
+ * leveraging Kotlin reified type parameters. This extension is not subject to type
+ * erasure and retains actual generic type arguments.
+ *
+ * @author Brian Clozel
+ * @since 2.0
+ */
+inline fun <reified T : Any> GraphQlClient.RetrieveSubscriptionSpec.toEntityList(): Flux<List<T>> =
+    toEntityList(object : ParameterizedTypeReference<T>() {})

spring-graphql/src/test/kotlin/org/springframework/graphql/client/GraphQlClientExtensionsTests.kt

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * 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.springframework.graphql.client
+
+import io.mockk.mockk
+import io.mockk.verify
+import org.junit.jupiter.api.Test
+import org.springframework.core.ParameterizedTypeReference
+
+
+/**
+ * Tests for [GraphQlClient] Kotlin extensions.
+ *
+ * @author Brian Clozel
+ */
+class GraphQlClientExtensionsTests {
+
+    private val retrieveSpec = mockk<GraphQlClient.RetrieveSpec>(relaxed = true)
+
+    private val retrieveSyncSpec = mockk<GraphQlClient.RetrieveSyncSpec>(relaxed = true)
+
+    private val retrieveSubscriptionSpec = mockk<GraphQlClient.RetrieveSubscriptionSpec>(relaxed = true)
+
+
+    @Test
+    fun `RetrieveSpec#toEntity with reified type parameters`() {
+        retrieveSpec.toEntity<Map<String, Book>>()
+        verify { retrieveSpec.toEntity(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    @Test
+    fun `RetrieveSpec#toEntityList with reified type parameters`() {
+        retrieveSpec.toEntityList<Book>()
+        verify { retrieveSpec.toEntityList(object : ParameterizedTypeReference<Book>() {}) }
+    }
+
+    @Test
+    fun `RetrieveSyncSpec#toEntity with reified type parameters`() {
+        retrieveSyncSpec.toEntity<Map<String, Book>>()
+        verify { retrieveSyncSpec.toEntity(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    @Test
+    fun `RetrieveSyncSpec#toEntityList with reified type parameters`() {
+        retrieveSyncSpec.toEntityList<Book>()
+        verify { retrieveSyncSpec.toEntityList(object : ParameterizedTypeReference<Book>() {}) }
+    }
+
+    @Test
+    fun `RetrieveSubscriptionSpec#toEntity with reified type parameters`() {
+        retrieveSubscriptionSpec.toEntity<Map<String, Book>>()
+        verify { retrieveSubscriptionSpec.toEntity(object : ParameterizedTypeReference<Map<String, Book>>() {}) }
+    }
+
+    @Test
+    fun `RetrieveSubscriptionSpec#toEntityList with reified type parameters`() {
+        retrieveSubscriptionSpec.toEntityList<Book>()
+        verify { retrieveSubscriptionSpec.toEntityList(object : ParameterizedTypeReference<Book>() {}) }
+    }
+
+
+    private class Book
+
+}