diff --git a/internal/repository/repo_test.go b/internal/repository/repo_test.go
new file mode 100644
index 0000000..552cc2e
--- /dev/null
+++ b/internal/repository/repo_test.go
@@ -0,0 +1,302 @@
+package repository
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type unrelatedKey struct{}
+
+func newTransactor(t *testing.T) (*Transactor, sqlmock.Sqlmock) {
+	t.Helper()
+
+	db, mock, err := sqlmock.New(sqlmock.QueryMatcherOption(sqlmock.QueryMatcherEqual))
+	require.NoError(t, err)
+
+	t.Cleanup(func() {
+		assert.NoError(t, mock.ExpectationsWereMet())
+		_ = db.Close()
+	})
+
+	return NewTransactor(db), mock
+}
+
+func TestNewRepo(t *testing.T) {
+	tr, _ := newTransactor(t)
+
+	repo := NewRepo(tr)
+
+	assert.Same(t, tr, repo.Transactor)
+}
+
+func TestRepo_Conn(t *testing.T) {
+	t.Run("falls back to the pool without a transaction", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+		repo := NewRepo(tr)
+
+		mock.ExpectExec("DELETE FROM users WHERE id = $1").
+			WithArgs("user-1").
+			WillReturnResult(sqlmock.NewResult(0, 1))
+
+		ctx := context.Background()
+		assert.Same(t, tr.db, repo.conn(ctx))
+
+		_, err := repo.conn(ctx).ExecContext(ctx, "DELETE FROM users WHERE id = $1", "user-1")
+		require.NoError(t, err)
+	})
+
+	t.Run("returns the transaction carried by the context", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+		repo := NewRepo(tr)
+
+		mock.ExpectBegin()
+		mock.ExpectRollback()
+
+		tx, err := tr.db.BeginTx(context.Background(), nil)
+		require.NoError(t, err)
+
+		ctx := context.WithValue(context.Background(), txKey{}, tx)
+		assert.Same(t, tx, repo.conn(ctx))
+
+		require.NoError(t, tx.Rollback())
+	})
+
+	t.Run("ignores values stored under other keys", func(t *testing.T) {
+		tr, _ := newTransactor(t)
+		repo := NewRepo(tr)
+
+		ctx := context.WithValue(context.Background(), unrelatedKey{}, "irrelevant")
+
+		assert.Same(t, tr.db, repo.conn(ctx))
+	})
+
+	t.Run("ignores a value of the wrong type under txKey", func(t *testing.T) {
+		tr, _ := newTransactor(t)
+		repo := NewRepo(tr)
+
+		ctx := context.WithValue(context.Background(), txKey{}, "not a transaction")
+
+		assert.Same(t, tr.db, repo.conn(ctx))
+	})
+}
+
+func TestRepo_WithinTxIsPromoted(t *testing.T) {
+	tr, mock := newTransactor(t)
+	repo := NewRepo(tr)
+
+	mock.ExpectBegin()
+	mock.ExpectExec("DELETE FROM users WHERE id = $1").
+		WithArgs("user-1").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+
+	err := repo.WithinTx(context.Background(), func(ctx context.Context) error {
+		_, execErr := repo.conn(ctx).ExecContext(ctx, "DELETE FROM users WHERE id = $1", "user-1")
+		return execErr
+	})
+
+	require.NoError(t, err)
+}
+
+func TestRepo_SiblingReposShareTheTransaction(t *testing.T) {
+	tr, mock := newTransactor(t)
+	users := NewRepo(tr)
+	lists := NewRepo(tr)
+
+	mock.ExpectBegin()
+	mock.ExpectExec("INSERT INTO lists (name) VALUES ($1)").
+		WithArgs("Groceries").
+		WillReturnResult(sqlmock.NewResult(1, 1))
+	mock.ExpectExec("DELETE FROM users WHERE id = $1").
+		WithArgs("user-1").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+
+	err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+		assert.Same(t, lists.conn(ctx), users.conn(ctx))
+
+		if _, err := lists.conn(ctx).ExecContext(ctx, "INSERT INTO lists (name) VALUES ($1)", "Groceries"); err != nil {
+			return err
+		}
+
+		_, err := users.conn(ctx).ExecContext(ctx, "DELETE FROM users WHERE id = $1", "user-1")
+		return err
+	})
+
+	require.NoError(t, err)
+}
+
+func TestTransactor_WithinTx(t *testing.T) {
+	t.Run("commits and routes statements through the tx", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+		repo := NewRepo(tr)
+
+		mock.ExpectBegin()
+		mock.ExpectExec("DELETE FROM users WHERE id = $1").
+			WithArgs("user-1").
+			WillReturnResult(sqlmock.NewResult(0, 1))
+		mock.ExpectCommit()
+
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			tx, ok := ctx.Value(txKey{}).(*sql.Tx)
+			require.True(t, ok)
+			assert.Same(t, tx, repo.conn(ctx))
+
+			_, execErr := repo.conn(ctx).ExecContext(ctx, "DELETE FROM users WHERE id = $1", "user-1")
+			return execErr
+		})
+
+		require.NoError(t, err)
+	})
+
+	t.Run("callback error rolls back and propagates", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		mock.ExpectBegin()
+		mock.ExpectRollback()
+
+		fnErr := errors.New("business rule violated")
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			return fnErr
+		})
+
+		assert.ErrorIs(t, err, fnErr)
+	})
+
+	t.Run("begin error skips the callback", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		beginErr := errors.New("too many connections")
+		mock.ExpectBegin().WillReturnError(beginErr)
+
+		called := false
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			called = true
+			return nil
+		})
+
+		assert.ErrorIs(t, err, beginErr)
+		assert.False(t, called)
+	})
+
+	t.Run("commit error is returned", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		commitErr := errors.New("could not serialize access")
+		mock.ExpectBegin()
+		mock.ExpectCommit().WillReturnError(commitErr)
+
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			return nil
+		})
+
+		assert.ErrorIs(t, err, commitErr)
+	})
+}
+
+func TestTransactor_WithinTxNested(t *testing.T) {
+	t.Run("reuses the outer tx and releases the savepoint", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		mock.ExpectBegin()
+		mock.ExpectExec("SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("RELEASE SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectCommit()
+
+		var outerTx *sql.Tx
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			outerTx = ctx.Value(txKey{}).(*sql.Tx)
+
+			return tr.WithinTx(ctx, func(ctx context.Context) error {
+				assert.Same(t, outerTx, ctx.Value(txKey{}).(*sql.Tx))
+				return nil
+			})
+		})
+
+		require.NoError(t, err)
+	})
+
+	t.Run("inner error rolls back to the savepoint", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		mock.ExpectBegin()
+		mock.ExpectExec("SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("ROLLBACK TO SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectRollback()
+
+		innerErr := errors.New("nested failure")
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			return tr.WithinTx(ctx, func(ctx context.Context) error {
+				return innerErr
+			})
+		})
+
+		assert.ErrorIs(t, err, innerErr)
+	})
+
+	t.Run("savepoint creation error skips the callback", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		spErr := errors.New("savepoint failed")
+		mock.ExpectBegin()
+		mock.ExpectExec("SAVEPOINT sp_1").WillReturnError(spErr)
+		mock.ExpectRollback()
+
+		called := false
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			return tr.WithinTx(ctx, func(ctx context.Context) error {
+				called = true
+				return nil
+			})
+		})
+
+		assert.ErrorIs(t, err, spErr)
+		assert.False(t, called)
+	})
+
+	t.Run("release error is returned", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		releaseErr := errors.New("no such savepoint")
+		mock.ExpectBegin()
+		mock.ExpectExec("SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("RELEASE SAVEPOINT sp_1").WillReturnError(releaseErr)
+		mock.ExpectRollback()
+
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			return tr.WithinTx(ctx, func(ctx context.Context) error {
+				return nil
+			})
+		})
+
+		assert.ErrorIs(t, err, releaseErr)
+	})
+
+	t.Run("each savepoint gets its own name", func(t *testing.T) {
+		tr, mock := newTransactor(t)
+
+		mock.ExpectBegin()
+		mock.ExpectExec("SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("RELEASE SAVEPOINT sp_1").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("SAVEPOINT sp_2").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectExec("RELEASE SAVEPOINT sp_2").WillReturnResult(sqlmock.NewResult(0, 0))
+		mock.ExpectCommit()
+
+		noop := func(ctx context.Context) error { return nil }
+
+		err := tr.WithinTx(context.Background(), func(ctx context.Context) error {
+			if err := tr.WithinTx(ctx, noop); err != nil {
+				return err
+			}
+			return tr.WithinTx(ctx, noop)
+		})
+
+		require.NoError(t, err)
+	})
+}