chore: add more tests (#3592)

core/iox/textlinescanner_test.go

@@ -3,6 +3,7 @@ package iox
 import (
 	"strings"
 	"testing"
+	"testing/iotest"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -22,3 +23,10 @@ func TestScanner(t *testing.T) {
 	}
 	assert.EqualValues(t, []string{"1", "2", "3", "4"}, lines)
 }
+
+func TestBadScanner(t *testing.T) {
+	scanner := NewTextLineScanner(iotest.ErrReader(iotest.ErrTimeout))
+	assert.False(t, scanner.Scan())
+	_, err := scanner.Line()
+	assert.ErrorIs(t, err, iotest.ErrTimeout)
+}