Include test case for regular subtransactions

While using COPY and subtransactions I kept running into errors.
This test case documents that error, it currently fails with:

    Error: encountered unexpected or invalid data: expecting ParseComplete but received CommandComplete

tests/postgres/postgres.rs

@@ -1,12 +1,15 @@
-use futures::{StreamExt, TryStreamExt};
+use futures::{Stream, StreamExt, TryStreamExt};
+
 use sqlx::postgres::types::Oid;
 use sqlx::postgres::{
     PgAdvisoryLock, PgConnectOptions, PgConnection, PgDatabaseError, PgErrorPosition, PgListener,
     PgPoolOptions, PgRow, PgSeverity, Postgres,
 };
 use sqlx::{Column, Connection, Executor, Row, Statement, TypeInfo};
+use sqlx_core::bytes::Bytes;
 use sqlx_test::{new, pool, setup_if_needed};
 use std::env;
+use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -382,6 +385,100 @@ async fn it_can_query_all_scalar() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[sqlx_macros::test]
+async fn copy_can_work_with_failed_subtransactions() -> anyhow::Result<()> {
+    let mut conn = new::<Postgres>().await?;
+
+
+    // We're using a (local) statement_timeout to simulate a runtime failure, as opposed to
+    // a parse/plan failure.
+    let mut tx = conn.begin().await?;
+    let _ = sqlx::query("SELECT pg_catalog.set_config($1, $2, true)")
+        .bind("statement_timeout")
+        .bind("1ms")
+        .execute(tx.as_mut())
+        .await?;
+
+    let mut sub_tx = tx.begin().await?;
+
+    let mut copy_out: Pin<
+        Box<dyn Stream<Item = Result<Bytes, sqlx::Error>> + Send>,
+    > = (&mut sub_tx)
+        .copy_out_raw("COPY (SELECT nspname FROM pg_catalog.pg_namespace WHERE pg_sleep(0.001) IS NULL) TO STDOUT")
+        .await?;
+
+    while copy_out.try_next().await.is_ok() {}
+    drop(copy_out);
+
+    sub_tx.rollback().await?;
+
+    // tx should be usable again, as we explictly rolled back the sub transaction
+    let got: i64 = sqlx::query_scalar("SELECT 1")
+        .fetch_one(tx.as_mut())
+        .await?;
+    assert_eq!(1, got);
+
+    Ok(())
+}
+
+#[sqlx_macros::test]
+async fn it_can_work_with_failed_subtransactions() -> anyhow::Result<()> {
+    let mut conn = new::<Postgres>().await?;
+
+    let mut tx = conn.begin().await?;
+
+    // We're using a (local) statement_timeout to simulate a runtime failure, as opposed to
+    // a parse/plan failure.
+    const KEY: &str = "statement_timeout";
+    const OUTER: &str = "10ms";
+    const INNER: &str = "1ms";
+    // By setting a local configuration parameter, we should test that we only
+    // rollback the subtx, not the outer tx.
+    let _ = sqlx::query("SELECT pg_catalog.set_config($1, $2, true)")
+        .bind(KEY)
+        .bind(OUTER)
+        .execute(tx.as_mut())
+        .await?;
+    let got: String = sqlx::query_scalar("SELECT current_setting($1)")
+        .bind(KEY)
+        .fetch_one(tx.as_mut())
+        .await?;
+
+    assert_eq!(OUTER, got.as_str());
+
+    let mut sub_tx = tx.begin().await?;
+    let _ = sqlx::query("SELECT pg_catalog.set_config($1, $2, true)")
+        .bind(KEY)
+        .bind(INNER)
+        .execute(sub_tx.as_mut())
+        .await?;
+
+    let got: String = sqlx::query_scalar("SELECT current_setting($1)")
+        .bind(KEY)
+        .fetch_one(sub_tx.as_mut())
+        .await?;
+
+    assert_eq!(INNER, got.as_str());
+
+    let a = sqlx::query("SELECT pg_sleep(0.02)")
+        .fetch_one(sub_tx.as_mut())
+        .await;
+    assert!(a.is_err());
+    // sub tx is unusable currently
+    let a = sqlx::query("SELECT 1").fetch_one(sub_tx.as_mut()).await;
+    assert!(a.is_err());
+    sub_tx.rollback().await?;
+
+    let got: String = sqlx::query_scalar("SELECT current_setting($1)")
+        .bind(KEY)
+        .fetch_one(tx.as_mut())
+        .await?;
+    assert_eq!(OUTER, got.as_str());
+    tx.rollback().await?;
+
+    Ok(())
+}
+
 #[sqlx_macros::test]
 async fn it_can_work_with_transactions() -> anyhow::Result<()> {
     let mut conn = new::<Postgres>().await?;