test: added tests for M2M relationships, it works

tests/m2m_relationship.rs

@@ -0,0 +1,20 @@
+use georm::Georm;
+
+mod models;
+use models::*;
+
+#[sqlx::test(fixtures("simple_struct", "o2o", "m2m"))]
+async fn genres_should_be_able_to_access_all_books(pool: sqlx::PgPool) -> sqlx::Result<()> {
+    let fantasy = Genre::find(&pool, &1).await?.unwrap();
+    let books = fantasy.get_books(&pool).await?;
+    assert_eq!(3, books.len());
+    Ok(())
+}
+
+#[sqlx::test(fixtures("simple_struct", "o2o", "m2m"))]
+async fn books_should_be_able_to_access_their_genres(pool: sqlx::PgPool) -> sqlx::Result<()> {
+    let to_build_a_fire = Book::find(&pool, &4).await?.unwrap();
+    let genres = to_build_a_fire.get_genres(&pool).await?;
+    assert_eq!(2, genres.len());
+    Ok(())
+}