add unit tests for DatabaseError downcasting

sqlx-core/src/mysql/error.rs

@@ -43,3 +43,22 @@ impl From<MySqlError> for crate::Error {
         crate::Error::Database(Box::new(err))
     }
 }
+
+#[test]
+fn test_error_downcasting() {
+    let error = MySqlError(ErrPacket {
+        error_code: 0xABCD,
+        sql_state: None,
+        error_message: "".into()
+    });
+
+    let error = crate::Error::from(error);
+
+    let db_err = match error {
+        crate::Error::Database(db_err) => db_err,
+        e => panic!("expected crate::Error::Database, got {:?}", e)
+    };
+
+    assert_eq!(db_err.downcast_ref::<MySqlError>().0.error_code, 0xABCD);
+    assert_eq!(db_err.downcast::<MySqlError>().0.error_code, 0xABCD);
+}

sqlx-core/src/postgres/error.rs

@@ -63,3 +63,38 @@ impl From<PgError> for crate::Error {
         crate::Error::Database(Box::new(err))
     }
 }
+
+#[test]
+fn test_error_downcasting() {
+    use super::protocol::Severity;
+
+    let error = PgError(Response {
+        severity: Severity::Panic,
+        code: "".into(),
+        message: "".into(),
+        detail: None,
+        hint: None,
+        position: None,
+        internal_position: None,
+        internal_query: None,
+        where_: None,
+        schema: None,
+        table: None,
+        column: None,
+        data_type: None,
+        constraint: None,
+        file: None,
+        line: None,
+        routine: None
+    });
+
+    let error = crate::Error::from(error);
+
+    let db_err = match error {
+        crate::Error::Database(db_err) => db_err,
+        e => panic!("expected Error::Database, got {:?}", e)
+    };
+
+    assert_eq!(db_err.downcast_ref::<PgError>().0.severity, Severity::Panic);
+    assert_eq!(db_err.downcast::<PgError>().0.severity, Severity::Panic);
+}

sqlx-core/src/postgres/protocol/mod.rs

@@ -60,7 +60,7 @@ pub(crate) use message::Message;
 pub(crate) use notification_response::NotificationResponse;
 pub(crate) use parameter_description::ParameterDescription;
 pub(crate) use ready_for_query::ReadyForQuery;
-pub(crate) use response::Response;
+pub(crate) use response::{Response, Severity};
 pub(crate) use row_description::{Field, RowDescription};
 
 pub(crate) trait Write {

sqlx-core/src/postgres/protocol/response.rs

@@ -3,7 +3,7 @@ use std::str::{self, FromStr};
 
 use crate::postgres::database::Postgres;
 
-#[derive(Debug, Copy, Clone)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub(crate) enum Severity {
     Panic,
     Fatal,

sqlx-core/src/sqlite/error.rs

@@ -71,3 +71,21 @@ impl From<SqliteError> for crate::Error {
         crate::Error::Database(Box::new(err))
     }
 }
+
+#[test]
+fn test_error_downcasting() {
+    let error = SqliteError {
+        code: "SQLITE_ERR_SOMETHING".into(),
+        message: "Some hypothetical error message".into()
+    };
+
+    let error = crate::Error::from(error);
+
+    let db_err = match error {
+        crate::Error::Database(db_err) => db_err,
+        e => panic!("expected Error::Database, got {:?}", e)
+    };
+
+    assert_eq!(&db_err.downcast_ref::<SqliteError>().code, "SQLITE_ERR_SOMETHING");
+    assert_eq!(db_err.downcast::<SqliteError>().code, "SQLITE_ERR_SOMETHING");
+}