diff --git a/spec/biju/pdu/gsm7bit_spec.rb b/spec/biju/pdu/gsm7bit_spec.rb
new file mode 100644
index 0000000..d10eaa5
--- /dev/null
+++ b/spec/biju/pdu/gsm7bit_spec.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+require 'biju/pdu/gsm7bit'
+
+describe Biju::PDU::GSM7Bit do
+  describe '::decode' do
+    it "decodes string" do
+      expect(Biju::PDU::GSM7Bit.decode('D4F29C0E', length: 4)).to eq('Test')
+    end
+
+    it "decodes character from extension set" do
+      expect(Biju::PDU::GSM7Bit.decode('9B32', length: 1)).to eq('€')
+    end
+
+    it "decodes character with a length of 7" do
+      expect(Biju::PDU::GSM7Bit.decode('E170381C0E8701', length: 7)).to eq('a' * 7)
+    end
+  end
+
+  describe '::encode' do
+    it "encodes string" do
+      expect(Biju::PDU::GSM7Bit.encode('Test').upcase).to eq('D4F29C0E')
+    end
+
+    it "encodes character from extension set" do
+      expect(Biju::PDU::GSM7Bit.encode('€').upcase).to eq('9B32')
+    end
+
+    it "encodes character with a length of 7" do
+      expect(Biju::PDU::GSM7Bit.encode('a' * 7).upcase).to eq('E170381C0E8701')
+    end
+  end
+
+  it "gives same text after encoding and decoding" do
+    strings = [
+      'My first TEST',
+      '{More complicated]',
+      'And on€ More~',
+      'a' * 7,
+    ]
+
+    strings.each do |string|
+      expect(Biju::PDU::GSM7Bit.decode(
+        Biju::PDU::GSM7Bit.encode(string), length: string.length)).to eq(string)
+    end
+  end
+end