diff --git a/src/test/kotlin/kestrel/store/codec/TupleCodecTest.kt b/src/test/kotlin/kestrel/store/codec/TupleCodecTest.kt
new file mode 100644
index 0000000..e82d8a3
--- /dev/null
+++ b/src/test/kotlin/kestrel/store/codec/TupleCodecTest.kt
@@ -0,0 +1,90 @@
+package kestrel.store.codec
+
+import java.math.BigDecimal
+import java.math.BigInteger
+import java.time.LocalDate
+import kestrel.storage.Value
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class TupleCodecTest {
+    @Test
+    fun roundTripsAllValueTypes() {
+        val row = listOf(
+            Value.IntegerValue(42),
+            Value.TextValue("hello world"),
+            Value.BooleanValue(true),
+            Value.RealValue(2.5),
+            Value.DecimalValue(BigDecimal("19.99")),
+            Value.DateValue(LocalDate.of(2024, 1, 15)),
+            Value.NullValue
+        )
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsDecimalExactlyPreservingScaleAndSign() {
+        val row = listOf(
+            Value.DecimalValue(BigDecimal.ZERO),
+            Value.DecimalValue(BigDecimal("-19.990")),
+            Value.DecimalValue(BigDecimal("1200")),
+            Value.DecimalValue(BigDecimal(BigInteger("123456789012345678901234567890"), 10))
+        )
+        val decoded = TupleCodec.decode(TupleCodec.encode(row))
+        assertEquals(row, decoded)
+        // Exact scale round-trip (not just numeric equality): -19.990 must stay 3-decimal, not collapse to -19.99.
+        assertEquals(3, (decoded[1] as Value.DecimalValue).value.scale())
+    }
+
+    @Test
+    fun roundTripsDatesIncludingBeforeTheEpoch() {
+        val row = listOf(
+            Value.DateValue(LocalDate.of(1970, 1, 1)),
+            Value.DateValue(LocalDate.of(1900, 1, 1)),
+            Value.DateValue(LocalDate.of(2999, 12, 31))
+        )
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsNegativeAndExtremeIntegers() {
+        val row = listOf(Value.IntegerValue(Long.MIN_VALUE), Value.IntegerValue(Long.MAX_VALUE), Value.IntegerValue(-1))
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsAllNullRow() {
+        val row = listOf(Value.NullValue, Value.NullValue, Value.NullValue)
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsEmptyRow() {
+        assertEquals(emptyList(), TupleCodec.decode(TupleCodec.encode(emptyList())))
+    }
+
+    @Test
+    fun nullBitmapSpansMultipleBytesForWideRows() {
+        val row = (0 until 20).map { if (it % 3 == 0) Value.NullValue else Value.IntegerValue(it.toLong()) }
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsUnicodeText() {
+        val row = listOf(Value.TextValue("zolw kruk ósmórog 🐦"))
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun roundTripsEmptyText() {
+        val row = listOf(Value.TextValue(""))
+        assertEquals(row, TupleCodec.decode(TupleCodec.encode(row)))
+    }
+
+    @Test
+    fun encodingIsCompactForSmallIntegers() {
+        val encoded = TupleCodec.encode(listOf(Value.IntegerValue(5)))
+        // 1 byte column count + 1 byte null bitmap + 1 byte tag + 1 byte zigzag payload
+        assertEquals(4, encoded.size)
+    }
+}