diff --git a/array.go b/array.go
index 5995365..5047832 100644
--- a/array.go
+++ b/array.go
@@ -139,6 +139,17 @@ func (a *Array) AddBinary(v *primitive.Binary) *Array {
 	return a
 }
 
+// AddUndefined
+func (a *Array) AddUndefined() *Array {
+	if a.d.immutable || !a.d.valid {
+		a.d.err = errImmutableInvalid
+		return a
+	}
+	a.d.AddUndefined(strconv.Itoa(a.n))
+	a.n++
+	return a
+}
+
 // AddOID ...
 func (a *Array) AddOID(v primitive.ObjectID) *Array {
 	if a.d.immutable || !a.d.valid {
diff --git a/array_test.go b/array_test.go
new file mode 100644
index 0000000..87d0438
--- /dev/null
+++ b/array_test.go
@@ -0,0 +1,158 @@
+package bsony
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"go.mongodb.org/mongo-driver/bson/primitive"
+)
+
+func testArrayAdd(t *testing.T, addCases []AddTestCase) {
+	// Array.Add is a wrapper around Doc.Add, so we can use the same input data.
+	t.Run("Array.Add", func(t *testing.T) {
+		for _, c := range addCases {
+			// replace key in document with "0" (ASCII 0x30)
+			aHex := c.D[0:10] + "30" + c.D[12:]
+
+			a := fct.NewArray()
+			a.Add(c.V)
+			compareArrayHex(t, a, aHex, c.L)
+			a.Release()
+		}
+	})
+
+	// Test adding to array with type-specific functions.  This is needed
+	// because Doc.Add delegates to the type-specific adders, but Array.Add
+	// delegates to Doc.Add.  Therefore, we have to do our own type-specific
+	// test for arrays.
+	t.Run("Array.AddType", func(t *testing.T) {
+		for _, c := range addCases {
+			// replace key in document with "0" (ASCII 0x30)
+			aHex := c.D[0:10] + "30" + c.D[12:]
+
+			a := fct.NewArray()
+			if addByType(a, c.V) {
+				compareArrayHex(t, a, aHex, c.L)
+			}
+			a.Release()
+		}
+	})
+
+}
+
+// Switch adapted from Doc.Add and will need to be kept in sync if new types
+// are added.
+func addByType(a *Array, v interface{}) bool {
+	switch x := v.(type) {
+	// Type 01 - double
+	case float32:
+		a.AddDouble(float64(x))
+	case float64:
+		a.AddDouble(x)
+
+	// Type 02 - string
+	case string:
+		a.AddString(x)
+
+	// Type 03 - document
+	case Doc:
+		a.AddDoc(&x)
+	case *Doc:
+		a.AddDoc(x)
+
+	// Type 04 - array
+	case Array:
+		a.AddArray(&x)
+	case *Array:
+		a.AddArray(x)
+
+	// Type 05 - binary
+	case primitive.Binary:
+		a.AddBinary(&x)
+	case *primitive.Binary:
+		a.AddBinary(x)
+
+	// Type 06 - undefined (deprecated)
+	case primitive.Undefined:
+		a.AddUndefined()
+
+	// Type 07 - ObjectID
+	case primitive.ObjectID:
+		a.AddOID(x)
+
+	// Type 08 - boolean
+	case bool:
+		a.AddBool(x)
+
+	// Type 09 - UTC DateTime
+	case primitive.DateTime:
+		a.AddDateTime(x)
+	case time.Time:
+		a.AddDateTimeFromTime(x)
+	case *time.Time:
+		a.AddDateTimeFromTime(*x)
+
+	// Type 0A - null
+	case nil:
+		a.AddNull()
+
+	// Type 0B - regular expression
+	case primitive.Regex:
+		a.AddRegex(x)
+	case *primitive.Regex:
+		a.AddRegex(*x)
+
+	// Type 0C - DBPointer (deprecated)
+	case primitive.DBPointer:
+		a.AddDBPointer(x)
+	case *primitive.DBPointer:
+		a.AddDBPointer(*x)
+
+	// Type 0D - JavaScript code
+	case primitive.JavaScript:
+		a.AddJavaScript(x)
+
+	// Type 0E - Symbol (deprecated)
+	case primitive.Symbol:
+		a.AddSymbol(x)
+
+		// Type 0F - JavaScript code with scope
+	case CodeWithScope:
+		a.AddCodeScope(x)
+	case primitive.CodeWithScope:
+		// AddCodeScope doesn't convert this, only Add, so skip test
+		return false
+
+	// Type 10 - 32-bit integer
+	case int32:
+		a.AddInt32(x)
+
+		// Type 11 - timestamp
+	case primitive.Timestamp:
+		a.AddTimestamp(x)
+
+	// Type 12 - 64-bit integer
+	case int64:
+		a.AddInt64(x)
+
+		// Type 13 - 128-bit decimal floating point
+	case primitive.Decimal128:
+		a.AddDecimal128(x)
+	case *primitive.Decimal128:
+		a.AddDecimal128(*x)
+
+	// Type FF - Min key
+	case primitive.MinKey:
+		a.AddMinKey()
+
+	// Type 7F - Max key
+	case primitive.MaxKey:
+		a.AddMaxKey()
+
+	default:
+		panic(fmt.Sprintf("unsupported type: %T", v))
+	}
+
+	return true
+}
diff --git a/document_test.go b/document_test.go
index e1437df..99756bc 100644
--- a/document_test.go
+++ b/document_test.go
@@ -46,6 +46,7 @@ const (
 	rfc3339Milli = "2006-01-02T15:04:05.999Z07:00"
 )
 
+// This function calls into array_test.go so as to use the same input data.
 func TestAdd(t *testing.T) {
 	fct := New()
 	testArray := fct.NewArray()
@@ -94,10 +95,15 @@ func TestAdd(t *testing.T) {
 		{"maxkey", "a", primitive.MaxKey{}, "080000007F610000"},
 	}
 
-	for _, c := range addCases {
-		d := fct.NewDoc()
-		d.Add(c.K, c.V)
-		compareDocHex(t, d, c.D, c.L)
-		d.Release()
-	}
+	t.Run("Doc.Add", func(t *testing.T) {
+		for _, c := range addCases {
+			d := fct.NewDoc()
+			d.Add(c.K, c.V)
+			compareDocHex(t, d, c.D, c.L)
+			d.Release()
+		}
+	})
+
+	// Delegate array testing with same data
+	testArrayAdd(t, addCases)
 }
diff --git a/util_test.go b/util_test.go
index 8400256..a5687ba 100644
--- a/util_test.go
+++ b/util_test.go
@@ -30,7 +30,7 @@ func compareArrayHex(t *testing.T, a *Array, want string, label string) {
 	got := strings.ToLower(hex.EncodeToString(a.d.buf))
 	want = strings.ToLower(want)
 	if got != want {
-		t.Errorf("%s: encoded doc incorrect.\nGot:  %s\nWant: %s", label, got, want)
+		t.Errorf("%s: encoded array incorrect.\nGot:  %s\nWant: %s", label, got, want)
 	}
 	return
 }