Added Cursor.At test

cursor/cursor_test.go

@@ -73,7 +73,17 @@ func testCursor[C cursor.Cursor[byte]](t *testing.T, makeCursor func([]byte) C)
 		test.ErrorIs(t, err, io.EOF)
 		test.EqOp(t, len(data), int(n))
 	}))
-	t.Run("At", Todo)
+	t.Run("At sets cursor position", rapid.MakeCheck(func(t *rapid.T) {
+		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
+		pos := rapid.Uint64Range(0, uint64(len(data)-1)).Draw(t, "pos")
+		c := makeCursor(data).At(pos)
+
+		dst := make([]byte, 1)
+		n, _, err := c.Read(dst)
+		test.EqOp(t, 1, n)
+		test.NoError(t, err)
+		test.EqOp(t, data[pos], dst[0])
+	}))
 }
 
 func TestSliceCursor(t *testing.T) {