package iox import ( "os" "testing" "github.com/stretchr/testify/assert" ) func TestCountLines(t *testing.T) { const val = `1 2 3 4` file, err := os.CreateTemp(os.TempDir(), "test-") if err != nil { t.Fatal(err) } defer os.Remove(file.Name()) file.WriteString(val) file.Close() lines, err := CountLines(file.Name()) assert.Nil(t, err) assert.Equal(t, 4, lines) } func TestCountLinesError(t *testing.T) { _, err := CountLines("not-exist") assert.NotNil(t, err) }