diff --git a/uint128be_test.go b/uint128be_test.go
new file mode 100644
index 0000000..4a172d0
--- /dev/null
+++ b/uint128be_test.go
@@ -0,0 +1,29 @@
+package unibase2n
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUint128be(t *testing.T) {
+	buf := [16]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
+	zero := readuint128be(make([]byte, 16))
+	one := readuint128be([]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1})
+	num := readuint128be(buf[:])
+	num.add(one)
+	assert.Equal(t, num, zero)
+	num.add(readuint128be([]byte{0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef, 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef}))
+	num.shr(8)
+	assert.Equal(t, num, &uint128be{0x001234567890abcd, 0xef1234567890abcd})
+	num.shr(16)
+	assert.Equal(t, num, &uint128be{0x0000001234567890, 0xabcdef1234567890})
+	num.shr(32)
+	assert.Equal(t, num, &uint128be{0x0000000000000012, 0x34567890abcdef12})
+	num.shr(1)
+	// 因为 num.a 低 1 位为 0 所以可以成功
+	assert.Equal(t, num, &uint128be{0x0000000000000012 >> 1, 0x34567890abcdef12 >> 1})
+	num.shr(7)
+	num.write(buf[:])
+	assert.Equal(t, buf, [16]byte{0, 0, 0, 0, 0, 0, 0, 0, 0x12, 0x34, 0x56, 0x78, 0x90, 0xab, 0xcd, 0xef})
+}