diff --git a/spec/apis/transactions_controller_spec.rb b/spec/apis/transactions_controller_spec.rb
index b11f596..32c7eb2 100644
--- a/spec/apis/transactions_controller_spec.rb
+++ b/spec/apis/transactions_controller_spec.rb
@@ -1,14 +1,21 @@
 describe TransactionsController, type: :api do
-  let(:api_attributes) do
-    {
-      debtor:   create(:user).name,
-      creditor: create(:user).name,
+  before :each do
+    @debtor   = create :user
+    @creditor = create :user
+    @api_attributes = {
+      debtor:   @debtor.name,
+      creditor: @creditor.name,
       message:  Faker::Lorem.sentence,
-      euros:    rand(2),
-      cents:    1 + rand(100)
+      euros:    1,
+      cents:    25
     }
   end
 
+  def post_transaction(extra_attributes = {})
+    post '/transactions', { transaction: @api_attributes.merge(extra_attributes) },
+        { 'HTTP_ACCEPT' => "application/json", "X_API_KEY" => @key }
+  end
+
   before :each do
     @client = Client.create name: "Tap"
     @key = @client.key
@@ -21,8 +28,31 @@ describe TransactionsController, type: :api do
     end
 
     it "should work with valid key" do
-      post '/transactions', { transaction: api_attributes }, { 'HTTP_ACCEPT' => "application/json", "X_API_KEY" => @key }
+      post_transaction
       expect(last_response.status).to eq(201)
     end
   end
+
+  describe "successfull creating transaction" do
+    it "should create a transaction" do
+      expect { post_transaction }.to change { Transaction.count }.by(1)
+    end
+
+    it "should set issuer" do
+      post_transaction
+      @transaction = Transaction.last
+      expect(@transaction.issuer).to eq(@client)
+    end
+  end
+
+  describe "failed creating transaction" do
+    it "should create a transaction" do
+      expect { post_transaction(euros: -5) }.to change { Transaction.count }.by(0)
+    end
+
+    it "should give 402 status" do
+      post_transaction(euros: -4)
+      expect(last_response.status).to eq(422)
+    end
+  end
 end