Add DB implementation with fault injection

core/db_test.go

@@ -1,11 +1,88 @@
 package core
 
 import (
+	"database/sql"
+	"errors"
+	"strings"
 	"testing"
 
 	_ "github.com/mattn/go-sqlite3"
 )
 
+type FailureDb struct {
+	db         DB
+	queryError func(string, ...any) error
+	execError  func(string, ...any) error
+}
+
+func (f *FailureDb) Query(query string, args ...any) (*sql.Rows, error) {
+	if f.queryError != nil {
+		if err := f.queryError(query, args...); err != nil {
+			return nil, err
+		}
+	}
+	return f.db.Query(query, args...)
+}
+
+func (f *FailureDb) QueryRow(query string, args ...any) *sql.Row {
+	return f.db.QueryRow(query, args...)
+}
+
+func (f *FailureDb) Exec(query string, args ...any) (sql.Result, error) {
+	if f.execError != nil {
+		if err := f.execError(query, args...); err != nil {
+			return nil, err
+		}
+	}
+	return f.db.Exec(query, args...)
+}
+
+func (f *FailureDb) Prepare(query string) (*sql.Stmt, error) {
+	return f.db.Prepare(query)
+}
+
+func (f *FailureDb) Transact(txFunc func(DB) error) error {
+	return f.db.Transact(func(tx DB) error {
+		ftx := FailureDb{
+			db:         tx,
+			queryError: f.queryError,
+			execError:  f.execError,
+		}
+		return txFunc(&ftx)
+	})
+}
+
+func TestFailureDb(t *testing.T) {
+	db := EphemeralDb(t)
+	fdb := FailureDb{
+		db: db,
+		queryError: func(q string, a ...any) error {
+			if strings.Contains(q, "2") {
+				return errors.New("oopsie")
+			}
+			return nil
+		},
+	}
+
+	if _, err := fdb.Query("select 1"); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := fdb.Query("select 2"); err == nil {
+		t.Fatal("expected error")
+	}
+
+	if err := fdb.Transact(func(tx DB) error {
+		if _, err := tx.Query("select 1"); err != nil {
+			t.Fatal(err)
+		}
+		_, err := tx.Query("select 2")
+		return err
+	}); err == nil {
+		t.Fatal("expected error from inside transaction")
+	}
+}
+
 func TestDeleteSourceCascade(t *testing.T) {
 	db := EphemeralDb(t)