Expose map of "extensions" in GraphQlRequest

This commit adds support for protocol, vendor specific protocol
extensions in the GraphQL client requests.

Closes gh-371

spring-graphql-test/src/main/java/org/springframework/graphql/test/tester/AbstractDirectGraphQlTransport.java

@@ -75,7 +75,7 @@ abstract class AbstractDirectGraphQlTransport implements GraphQlTransport {
 
 	private ExecutionGraphQlRequest toExecutionRequest(GraphQlRequest request) {
 		return new DefaultExecutionGraphQlRequest(
-				request.getDocument(), request.getOperationName(), request.getVariables(),
+				request.getDocument(), request.getOperationName(), request.getVariables(), request.getExtensions(),
 				idGenerator.generateId().toString(), null);
 	}
 

spring-graphql-test/src/main/java/org/springframework/graphql/test/tester/DefaultGraphQlTester.java

@@ -125,6 +125,8 @@ final class DefaultGraphQlTester implements GraphQlTester {
 
 		private final Map<String, Object> variables = new LinkedHashMap<>();
 
+		private final Map<String, Object> extensions = new LinkedHashMap<>();
+
 		private DefaultRequest(String document) {
 			Assert.notNull(document, "`document` is required");
 			this.document = document;
@@ -142,6 +144,12 @@ final class DefaultGraphQlTester implements GraphQlTester {
 			return this;
 		}
 
+		@Override
+		public DefaultRequest extension(String name, Object value) {
+			this.extensions.put(name, value);
+			return this;
+		}
+
 		@SuppressWarnings("ConstantConditions")
 		@Override
 		public Response execute() {
@@ -159,7 +167,7 @@ final class DefaultGraphQlTester implements GraphQlTester {
 		}
 
 		private GraphQlRequest request() {
-			return new DefaultGraphQlRequest(this.document, this.operationName, this.variables);
+			return new DefaultGraphQlRequest(this.document, this.operationName, this.variables, this.extensions);
 		}
 
 		private DefaultResponse mapResponse(GraphQlResponse response, GraphQlRequest request) {

spring-graphql-test/src/main/java/org/springframework/graphql/test/tester/GraphQlTester.java

@@ -149,6 +149,15 @@ public interface GraphQlTester {
 		 */
 		T variable(String name, @Nullable Object value);
 
+		/**
+		 * Add a variable.
+		 * @param name the variable name
+		 * @param value the variable value, possibly {@code null} since GraphQL
+		 * supports providing null value vs not providing a value at all.
+		 * @return this request spec
+		 */
+		T extension(String name, @Nullable Object value);
+
 		/**
 		 * Execute the GraphQL request and return a spec for further inspection of
 		 * response data and errors.

spring-graphql-test/src/test/java/org/springframework/graphql/test/tester/GraphQlTesterTests.java

@@ -217,6 +217,23 @@ public class GraphQlTesterTests extends GraphQlTesterTestSupport {
 		assertThat(request.getVariables()).containsEntry("keyOnly", null);
 	}
 
+	@Test
+	void protocolExtensions() {
+		String document = "{me {name, friends}}";
+		getGraphQlService().setDataAsJson(document, "{\"me\": {\"name\":\"Luke Skywalker\", \"friends\":[]}}");
+
+		graphQlTester().document(document)
+				.extension("firstExt", Collections.singletonMap("key", "value"))
+				.extension("secondExt", "value")
+				.execute();
+
+		ExecutionGraphQlRequest request = getGraphQlService().getGraphQlRequest();
+		assertThat(request.getDocument()).contains(document);
+		assertThat(request.getExtensions()).hasSize(2);
+		assertThat(request.getExtensions()).containsEntry("firstExt", Collections.singletonMap("key", "value"))
+				.containsEntry("secondExt", "value");
+	}
+
 	@Test
 	void errorsEmptyOnExecuteAndVerify() {