1 files changed, 21 insertions, 0 deletions
diff --git a/mountain_pass/extract_test.go b/mountain_pass/extract_test.go
index 636372c..7eae33b 100644
--- a/mountain_pass/extract_test.go
+++ b/mountain_pass/extract_test.go
@@ -1,10 +1,13 @@
 package mountain_pass
 
 import (
+	"io"
+	"strings"
 	"testing"
 
 	"github.com/paulmach/osm"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestIsMountainPass(t *testing.T) {
@@ -47,3 +50,21 @@ func TestParseElevation(t *testing.T) {
 		assert.Equal(t, c.ok, ok)
 	}
 }
+
+func TestCountingReaderTracksBytes(t *testing.T) {
+	const content = "0123456789abcdef"
+	reader := &countingReader{r: strings.NewReader(content)}
+
+	buf := make([]byte, 4)
+	var total int64
+	for {
+		n, err := reader.Read(buf)
+		total += int64(n)
+		require.Equal(t, total, reader.n)
+		if err == io.EOF {
+			break
+		}
+		require.NoError(t, err)
+	}
+	assert.Equal(t, int64(len(content)), reader.n)
+}