Improve readability of assertion messages

Closes gh-361

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/support/DefaultExecutionGraphQlResponse.java

@@ -152,6 +152,11 @@ public Map<String, Object> getExtensions() {
 			return (this.delegate.getExtensions() != null ? this.delegate.getExtensions() : Collections.emptyMap());
 		}
 
+		@Override
+		public String toString() {
+			return this.delegate.toString();
+		}
+
 	}
 
 

spring-graphql/src/test/java/org/springframework/graphql/client/GraphQlClientTests.java

@@ -205,7 +205,8 @@ void executePartialResponse() {
 		assertThat(nameField.getError().getParsedPath()).containsExactly("me", "name");
 		assertThatThrownBy(() -> nameField.toEntity(String.class))
 				.as("Decoding field null with direct field error should be rejected")
-				.isInstanceOf(FieldAccessException.class);
+				.isInstanceOf(FieldAccessException.class)
+				.hasMessageContaining("Test error");
 
 		ClientResponseField nonExistingField = response.field("me.name.other");
 		assertThat(nonExistingField.hasValue()).isFalse();