Add a test of spreads (#776)

cynic/tests/snapshots/spread__snapshot_test_query.snap

@@ -0,0 +1,19 @@
+---
+source: cynic/tests/spread.rs
+expression: query.query
+---
+query FilmDirectorQuery($id: ID) {
+  film(id: $id) {
+    id
+    __typename
+    ... {
+      title
+      director
+    }
+    ... {
+      releaseDate
+    }
+  }
+}
+
+

cynic/tests/spread.rs

@@ -0,0 +1,69 @@
+#![allow(dead_code)]
+
+mod schema {
+    cynic::use_schema!("../schemas/starwars.schema.graphql");
+}
+
+#[derive(cynic::QueryFragment, Debug)]
+#[cynic(
+    graphql_type = "Film",
+    schema_path = "../schemas/starwars.schema.graphql"
+)]
+struct FilmDetails {
+    title: Option<String>,
+    director: Option<String>,
+}
+
+#[derive(cynic::QueryFragment, Debug)]
+#[cynic(
+    graphql_type = "Film",
+    schema_path = "../schemas/starwars.schema.graphql"
+)]
+struct FilmMoreDetails {
+    release_date: Option<String>,
+}
+
+#[derive(cynic::QueryFragment, Debug)]
+#[cynic(schema_path = "../schemas/starwars.schema.graphql")]
+struct Film {
+    id: cynic::Id,
+    #[cynic(spread)]
+    details: FilmDetails,
+    #[cynic(spread)]
+    more_details: FilmMoreDetails,
+}
+
+#[derive(cynic::QueryVariables)]
+struct FilmArguments {
+    id: Option<cynic::Id>,
+}
+
+#[derive(cynic::QueryFragment, Debug)]
+#[cynic(
+    graphql_type = "Root",
+    variables = "FilmArguments",
+    schema_path = "../schemas/starwars.schema.graphql"
+)]
+struct FilmDirectorQuery {
+    #[arguments(id: $id)]
+    film: Option<Film>,
+}
+
+fn build_query() -> cynic::Operation<FilmDirectorQuery, FilmArguments> {
+    use cynic::QueryBuilder;
+
+    FilmDirectorQuery::build(FilmArguments {
+        id: Some("ZmlsbXM6MQ==".into()),
+    })
+}
+
+#[test]
+fn snapshot_test_query() {
+    // Running a snapshot test of the query building functionality as that gives us
+    // a place to copy and paste the actual GQL we're using for running elsewhere,
+    // and also helps ensure we don't change queries by mistake
+
+    let query = build_query();
+
+    insta::assert_snapshot!(query.query);
+}