Merge #3

3: Return correct value from maskRing.Shift r=antifuchs a=antifuchs

As @jsnell correctly notes in #1, we're not returning the right index value there when shifting from a ring that has already gone around once.

This PR adds a test and fixes #1.

Co-authored-by: Andreas Fuchs <[email protected]>

mask_ring.go

@@ -40,7 +40,7 @@ func (r *maskRing) Shift() (uint, error) {
 	}
 	i := r.read
 	r.read++
-	return i, nil
+	return r.Mask(i), nil
 }
 
 func (r *maskRing) Size() uint {

ring_test.go

@@ -4,10 +4,38 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestForcePush(t *testing.T) {
 	r := NewRing(1)
 	r.Push()
 	assert.Equal(t, ForcePush(r), uint(0))
 }
+
+func TestPushAndShift(t *testing.T) {
+	tests := []struct {
+		name  string
+		cap   uint
+		turns uint
+	}{
+		{"mask/3", 16, 3},
+		{"basic/3", 19, 3},
+	}
+	for _, elt := range tests {
+		test := elt
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			ring := NewRing(test.cap)
+			for i := uint(0); i < test.cap*test.turns; i++ {
+				pushed, err := ring.Push()
+				require.NoError(t, err)
+				require.True(t, pushed < test.cap)
+
+				shifted, err := ring.Shift()
+				require.NoError(t, err)
+				require.Equal(t, pushed, shifted, "on attempt %d", i)
+			}
+		})
+	}
+}