diff --git a/spec/biju/pdu/data_coding_scheme_spec.rb b/spec/biju/pdu/data_coding_scheme_spec.rb
new file mode 100644
index 0000000..184a23a
--- /dev/null
+++ b/spec/biju/pdu/data_coding_scheme_spec.rb
@@ -0,0 +1,29 @@
+require 'spec_helper'
+require 'biju/pdu'
+
+describe Biju::PDU::DataCodingScheme do
+  describe '::autodetect' do
+    it "autodetects gsm7bit encoding" do
+      [
+        "Test",
+        "Ç$",
+        "[teßt}",
+      ].each do |string|
+        expect(Biju::PDU::DataCodingScheme.autodetect(string)).to eq(:gsm7bit)
+      end
+    end
+
+    it "autodetects ucs2 encoding" do
+      [
+        "ç",
+        "âmazing",
+      ].each do |string|
+        expect(Biju::PDU::DataCodingScheme.autodetect(string)).to eq(:ucs2)
+      end
+    end
+  end
+
+  subject { Biju::PDU::DataCodingScheme.new(:gsm7bit) }
+  its(:to_sym) { should eq(:gsm7bit) }
+  its(:hex) { should eq(0) }
+end
diff --git a/spec/biju/pdu/phone_number_spec.rb b/spec/biju/pdu/phone_number_spec.rb
new file mode 100644
index 0000000..3943fe1
--- /dev/null
+++ b/spec/biju/pdu/phone_number_spec.rb
@@ -0,0 +1,21 @@
+require 'spec_helper'
+require 'biju/pdu'
+
+describe Biju::PDU::PhoneNumber do
+  describe '::encode' do
+    subject { Biju::PDU::PhoneNumber.encode('33123456789') }
+    its(:number) { should eq('3321436587F9') }
+  end
+
+  context "odd length" do
+    subject { Biju::PDU::PhoneNumber.new('3321436587F9') }
+    its(:decode) { should eq('33123456789') }
+    its(:length) { should eq(11) }
+  end
+
+  context "even length" do
+    subject { Biju::PDU::PhoneNumber.new('3321436587') }
+    its(:decode) { should eq('3312345678') }
+    its(:length) { should eq(10) }
+  end
+end
diff --git a/spec/biju/pdu/type_of_address_spec.rb b/spec/biju/pdu/type_of_address_spec.rb
new file mode 100644
index 0000000..6312dcd
--- /dev/null
+++ b/spec/biju/pdu/type_of_address_spec.rb
@@ -0,0 +1,9 @@
+require 'spec_helper'
+require 'biju/pdu'
+
+describe Biju::PDU::TypeOfAddress do
+  subject { Biju::PDU::TypeOfAddress.new(:international) }
+
+  its(:to_sym) { should eq(:international) }
+  its(:hex) { should eq(145) }
+end
diff --git a/spec/biju/pdu/user_data_spec.rb b/spec/biju/pdu/user_data_spec.rb
new file mode 100644
index 0000000..9d7bc52
--- /dev/null
+++ b/spec/biju/pdu/user_data_spec.rb
@@ -0,0 +1,12 @@
+require 'spec_helper'
+require 'biju/pdu'
+
+describe Biju::PDU::UserData do
+  subject(:message) { 'Test' }
+  subject(:encoded) { Biju::PDU::Encoding::GSM7Bit.encode(message) }
+  subject { Biju::PDU::UserData.encode(message, encoding: :gsm7bit) }
+
+  its(:message) { should eq(encoded[0]) }
+  its(:length) { should eq(encoded[1][:length]) }
+  its(:decode) { should eq(message) }
+end
diff --git a/spec/biju/sms_spec.rb b/spec/biju/sms_spec.rb
index f3ade4a..a2f262e 100644
--- a/spec/biju/sms_spec.rb
+++ b/spec/biju/sms_spec.rb
@@ -23,5 +23,18 @@ describe Biju::Sms do
 
     its(:datetime) { should eq(DateTime.new(2013, 9, 5, 9, 59, 29, '+08')) }
     its(:message) { should eq('Test') }
+    its(:phone_number) { should eq('33666666666') }
+    its(:type_of_address) { should eq(:international) }
+  end
+
+  describe '#to_pdu' do
+    subject do
+      Biju::Sms.new(
+        phone_number: '33666666666',
+        type_of_address: :international,
+        message: 'Test').to_pdu.upcase
+    end
+
+    it { should eq('0001000B913366666666F6000004D4F29C0E') }
   end
 end