diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..45a9174
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,2 @@
+Metrics/BlockLength:
+  Enabled: false
diff --git a/Dockerfile b/Dockerfile
index 1f4b90b..ba95a06 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -5,4 +5,4 @@ COPY . /usr/src/app
 
 RUN cd /usr/src/app && bundle install
 
-ENTRYPOINT ["ruby", "/usr/src/app/app.rb"]
\ No newline at end of file
+ENTRYPOINT ["/usr/src/app/entrypoint.sh"]
diff --git a/Gemfile b/Gemfile
index b5aabfc..e72c38f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,9 @@
 source 'https://rubygems.org' do
   gem 'aws-sdk-states'
-end
\ No newline at end of file
+
+  group :test do
+    gem 'nokogiri'
+    gem 'rspec'
+    gem 'rspec-mocks'
+  end
+end
diff --git a/Gemfile.lock b/Gemfile.lock
index 7d84981..bc02bca 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -16,13 +16,34 @@ GEM
       aws-sigv4 (~> 1.1)
     aws-sigv4 (1.5.2)
       aws-eventstream (~> 1, >= 1.0.2)
+    diff-lcs (1.5.1)
     jmespath (1.6.2)
+    nokogiri (1.16.2-arm64-darwin)
+      racc (~> 1.4)
+    racc (1.7.3)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.0)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.1)
 
 PLATFORMS
   arm64-darwin-21
+  arm64-darwin-23
 
 DEPENDENCIES
   aws-sdk-states!
+  nokogiri!
+  rspec!
+  rspec-mocks!
 
 BUNDLED WITH
    2.3.7
diff --git a/app.rb b/app.rb
index 0ce4a5a..1605a5e 100644
--- a/app.rb
+++ b/app.rb
@@ -1,6 +1,12 @@
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift File.expand_path('.', 'lib')
+
 require 'aws-sdk-states'
 require 'json'
 
+require 'deployment'
+
 STDOUT.sync = true
 
 execution_arn = ENV['EXECUTION_ARN']
@@ -12,60 +18,21 @@
 
 aws_client = Aws::States::Client.new(region: 'eu-west-1')
 
-def deployment_status(aws_client, execution_arn)
-  aws_client.describe_execution({ execution_arn: execution_arn }).status
-end
-
-def failure_reason(aws_client, execution_arn)
-  resp = aws_client.get_execution_history({
-    execution_arn: execution_arn,
-    max_results: 2,
-    reverse_order: true
-  })
-
-  event_type = resp.events[1].type
-  if event_type == "LambdaFunctionFailed"
-    error_message = JSON.parse(resp.events[1].lambda_function_failed_event_details.cause)['errorMessage']
-    if error_message.include? "Pre flight checks failed"
-      preflight_checks_output = error_message.lines[1]
-      forward_deploy_check_result =  preflight_checks_output.match(/ForwardDeployCheck=>"(.*?)"/i).captures[0]
-      if forward_deploy_check_result == "FAILED"
-        deploy_fail_reason = "Forward deploy check FAILED. No need to panic! "\
-                             "This likely means your commit has already been deployed as part of a previous deploy. "\
-                             "To confirm you can check whether your SHA is a parent commit to the currently deployed SHA. "\
-                             "You can figure out the currently deployed SHA by following this guide https://www.notion.so/freeagent/Deployment-Runbooks-29796221387e40b7abbb217d7d33c4ac?pvs=4#3bfa2ab5d3ab4c33b7a46522027f94bb"
-        return deploy_fail_reason
-      end
-    end
-    deploy_fail_reason = error_message
-  elsif event_type == "FailStateEntered"
-    error_message = JSON.parse(JSON.parse(resp.events[1].state_entered_event_details.input)['Error']['Cause'])['errorMessage']
-    if error_message.include? "ECS" and error_message.include? "IN_PROGRESS"
-      deploy_fail_reason = "Sidekiq workers failed to start or failed to stabilise."
-    else
-      deploy_fail_reason = "Failure message: #{error_message}. Please investigate further here if required https://eu-west-1.console.aws.amazon.com/states/home?region=eu-west-1#/executions/details/#{execution_arn}"
-    end
-  else
-    deploy_fail_reason = "Uncaught failure. Please investigate here https://eu-west-1.console.aws.amazon.com/states/home?region=eu-west-1#/executions/details/#{execution_arn}"
-  end
-
-  return deploy_fail_reason
-end
+deploy = Deployment::Deployment.new(aws_client, execution_arn)
 
-# One of: "RUNNING", "SUCCEEDED", "FAILED", "TIMED_OUT", "ABORTED"
-if deployment_status(aws_client, execution_arn) == 'RUNNING'
+if deploy.running?
   puts 'Deployment in progress...🔄'
   puts "Monitor at https://eu-west-1.console.aws.amazon.com/states/home?region=eu-west-1#/executions/details/#{execution_arn}"
-  sleep 15 until deployment_status(aws_client, execution_arn) != 'RUNNING'
 end
 
-deploy_status = deployment_status(aws_client, execution_arn)
-if %w[FAILED TIMED_OUT ABORTED].include?(deploy_status)
-  puts "Deployment Failure Status: #{deploy_status} ❌"
+sleep 10 while deploy.running?
+
+if deploy.succeeded?
+  puts 'Deployment Successful 🎉'
+else
+  puts "Deployment Failure Status: #{deploy.status} ❌"
   File.open(ENV['GITHUB_OUTPUT'], 'a') do |f|
-    f.puts "deployment_failed=true"
-    f.puts "deployment_failure_reason=#{failure_reason(aws_client, execution_arn)}"
+    f.puts 'deployment_failed=true'
+    f.puts "deployment_failure_reason=#{deploy.failure_reason}"
   end
-elsif deploy_status == 'SUCCEEDED'
-  puts 'Deployment Successful 🎉'
 end
diff --git a/entrypoint.sh b/entrypoint.sh
new file mode 100755
index 0000000..7b62309
--- /dev/null
+++ b/entrypoint.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+cd /usr/src/app && bundle exec ruby app.rb
diff --git a/lib/deployment.rb b/lib/deployment.rb
new file mode 100644
index 0000000..7df44f4
--- /dev/null
+++ b/lib/deployment.rb
@@ -0,0 +1,3 @@
+require 'deployment/deployment'
+require 'deployment/events/fail_state_entered'
+require 'deployment/events/lambda_function_failed'
diff --git a/lib/deployment/deployment.rb b/lib/deployment/deployment.rb
new file mode 100644
index 0000000..59abd6e
--- /dev/null
+++ b/lib/deployment/deployment.rb
@@ -0,0 +1,61 @@
+module Deployment
+  class Deployment
+    def initialize(aws_client, execution_arn)
+      @aws_client = aws_client
+      @execution_arn = execution_arn
+    end
+
+    def status
+      @aws_client.describe_execution({ execution_arn: @execution_arn }).status
+    end
+
+    def running?
+      status == 'RUNNING'
+    end
+
+    def succeeded?
+      status == 'SUCCEEDED'
+    end
+
+    def aborted?
+      status == 'ABORTED'
+    end
+
+    def timed_out?
+      status == 'TIMED_OUT'
+    end
+
+    def failed?
+      status == 'FAILED'
+    end
+
+    def failure_reason
+      raise 'Deploy still runnning' if running?
+      raise 'Deploy succeeded' if succeeded?
+
+      event_type = fail_event.type
+
+      case event_type
+      when 'LambdaFunctionFailed'
+        Events::LambdaFunctionFailed.new(fail_event).error
+      when 'FailStateEntered'
+        Events::FailStateEntered.new(fail_event, @execution_arn).error
+      else
+        "Uncaught failure. Please investigate here https://eu-west-1.console.aws.amazon.com/states/home?region=eu-west-1#/executions/details/#{@execution_arn}"
+      end
+    end
+
+    private
+
+    def fail_event
+      # The penultimate event holds the failure reason
+      @aws_client.get_execution_history(
+        {
+          execution_arn: @execution_arn,
+          max_results: 2,
+          reverse_order: true
+        }
+      ).events.last
+    end
+  end
+end
diff --git a/lib/deployment/events/fail_state_entered.rb b/lib/deployment/events/fail_state_entered.rb
new file mode 100644
index 0000000..c14c5d8
--- /dev/null
+++ b/lib/deployment/events/fail_state_entered.rb
@@ -0,0 +1,36 @@
+module Deployment
+  module Events
+    class FailStateEntered
+      def initialize(event, execution_arn)
+        @event = event
+        @execution_arn = execution_arn
+      end
+
+      def error
+        if sidekiq_error?
+          'Sidekiq workers failed to start or failed to stabilise.'
+        else
+          "Failure message: #{error_message}. Please investigate further here if required https://eu-west-1.console.aws.amazon.com/states/home?region=eu-west-1#/executions/details/#{@execution_arn}"
+        end
+      end
+
+      private
+
+      def error_message
+        @error_message ||= JSON.parse(JSON.parse(@event.state_entered_event_details.input)['Error']['Cause'])['errorMessage']
+      end
+
+      def in_progress?
+        error_message.include? 'IN_PROGRESS'
+      end
+
+      def ecs_error?
+        error_message.include? 'ECS'
+      end
+
+      def sidekiq_error?
+        ecs_error? && in_progress?
+      end
+    end
+  end
+end
diff --git a/lib/deployment/events/lambda_function_failed.rb b/lib/deployment/events/lambda_function_failed.rb
new file mode 100644
index 0000000..5d7618b
--- /dev/null
+++ b/lib/deployment/events/lambda_function_failed.rb
@@ -0,0 +1,42 @@
+module Deployment
+  module Events
+    class LambdaFunctionFailed
+      def initialize(event)
+        @event = event
+      end
+
+      def error
+        if preflight_checks_failed? && forward_deploy_check_failed?
+          'Forward deploy check FAILED. No need to panic! '\
+          'This likely means your commit has already been deployed as part of a previous deploy. '\
+          'To confirm you can check whether your SHA is a parent commit to the currently deployed SHA. '\
+          'You can figure out the currently deployed SHA by following this guide https://www.notion.so/freeagent/Deployment-Runbooks-29796221387e40b7abbb217d7d33c4ac?pvs=4#3bfa2ab5d3ab4c33b7a46522027f94bb'
+        else
+          error_message
+        end
+      end
+
+      private
+
+      def error_message
+        @error_message ||= JSON.parse(@event.lambda_function_failed_event_details.cause)['errorMessage']
+      end
+
+      def preflight_checks_output
+        error_message.lines[1]
+      end
+
+      def preflight_checks_failed?
+        error_message.include? 'Pre flight checks failed'
+      end
+
+      def forward_deploy_check_result
+        preflight_checks_output.match(/ForwardDeployCheck=>"(.*?)"/i).captures[0]
+      end
+
+      def forward_deploy_check_failed?
+        forward_deploy_check_result == 'FAILED'
+      end
+    end
+  end
+end
diff --git a/spec/app_spec.rb b/spec/app_spec.rb
new file mode 100644
index 0000000..9eb67e8
--- /dev/null
+++ b/spec/app_spec.rb
@@ -0,0 +1,117 @@
+require 'rspec'
+require 'stringio'
+
+require 'aws-sdk-states'
+
+RSpec.describe 'app' do
+  let(:mock_client) { double('Aws::States::Client') }
+  let(:execution_arn) { 'arn:aws:states:eu-west-1:123456789012:execution:my-execution-flow' }
+  let(:test_github_log) { Tempfile.new('github_output') }
+
+  before(:each) do
+    ENV['EXECUTION_ARN'] = execution_arn
+    ENV['GITHUB_OUTPUT'] = test_github_log.path
+    allow(Aws::States::Client).to receive(:new).and_return(mock_client)
+    allow(mock_client).to receive(:describe_execution).with(any_args).and_return(desc_exec_resp)
+    allow(mock_client).to receive(:get_execution_history).with(any_args).and_return(get_exec_history)
+  end
+
+  context 'when deployment was successful' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'SUCCEEDED') }
+    let(:get_exec_history) {}
+
+    it 'outputs "Deployment Successful 🎉"' do
+      $stdout = StringIO.new
+
+      # Execute the script
+      load "#{__dir__}/../app.rb"
+
+      # Assert the output
+      expect($stdout.string).to eq("Deployment Successful 🎉\n")
+    end
+  end
+
+  context 'when forward deploy check failed' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'FAILED') }
+    let(:get_exec_history) do
+      Aws::States::Types::GetExecutionHistoryOutput.new(
+        events: [
+          '',
+          Aws::States::Types::HistoryEvent.new(
+            type: 'LambdaFunctionFailed',
+            lambda_function_failed_event_details: Aws::States::Types::LambdaFunctionFailedEventDetails.new(
+              cause: '
+                {
+                  "errorMessage": "Pre flight checks failed:\n{\"Checks\"=>{:RequiredParameters=>\"PASSED\", :CommitCheck=>\"PASSED\", :ScheduleCheck=>\"PASSED\", :ForwardDeployCheck=>\"FAILED\"}, \"Status\"=>\"FAILED\"}",
+                  "errorType": "Function<StandardError>",
+                  "stackTrace": [
+                    "/var/task/pre_flight_checks.rb:145:in `handler"
+                  ]
+                }'
+            )
+          )
+        ]
+      )
+    end
+
+    it 'outputs that it failed' do
+      $stdout = StringIO.new
+
+      # Execute the script
+      load "#{__dir__}/../app.rb"
+
+      # Assert the output
+      expect($stdout.string).to eq("Deployment Failure Status: FAILED ❌\n")
+      expect(File.readlines(test_github_log.path)).to eq(
+        [
+          "deployment_failed=true\n",
+          'deployment_failure_reason=' \
+            'Forward deploy check FAILED. No need to panic! '\
+            'This likely means your commit has already been deployed as part of a previous deploy. '\
+            'To confirm you can check whether your SHA is a parent commit to the currently deployed SHA. '\
+            "You can figure out the currently deployed SHA by following this guide https://www.notion.so/freeagent/Deployment-Runbooks-29796221387e40b7abbb217d7d33c4ac?pvs=4#3bfa2ab5d3ab4c33b7a46522027f94bb\n"
+        ]
+      )
+    end
+  end
+
+  context 'when sidekiq failed to start' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'FAILED') }
+    let(:get_exec_history) do
+      Aws::States::Types::GetExecutionHistoryOutput.new(
+        events: [
+          '',
+          Aws::States::Types::HistoryEvent.new(
+            type: 'FailStateEntered',
+            state_entered_event_details: Aws::States::Types::StateEnteredEventDetails.new(
+              input: '
+                {
+                  "Error": {
+                    "Cause":"{\"errorMessage\":\"ECS deployment status: IN_PROGRESS\",\"errorType\":\"Function<DeployInProgress>\",\"stackTrace\":[\"/var/task/ecs_deployment_handler.rb:49:in `handler\"]}",
+                    "error":"Function<DeployInProgress>","resource":"invoke","resourceType":"lambda}"
+                  }
+                }
+              '
+            )
+          )
+        ]
+      )
+    end
+
+    it 'outputs that it failed' do
+      $stdout = StringIO.new
+
+      # Execute the script
+      load "#{__dir__}/../app.rb"
+
+      # Assert the output
+      expect($stdout.string).to eq("Deployment Failure Status: FAILED ❌\n")
+      expect(File.readlines(test_github_log.path)).to eq(
+        [
+          "deployment_failed=true\n",
+          "deployment_failure_reason=Sidekiq workers failed to start or failed to stabilise.\n"
+        ]
+      )
+    end
+  end
+end
diff --git a/spec/deployment_spec.rb b/spec/deployment_spec.rb
new file mode 100644
index 0000000..ceff5af
--- /dev/null
+++ b/spec/deployment_spec.rb
@@ -0,0 +1,208 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Deployment::Deployment do
+  subject(:deployment) { Deployment::Deployment.new(mock_client, execution_arn) }
+
+  let(:mock_client) { double('Aws::States::Client') }
+  let(:execution_arn) { 'arn:aws:states:eu-west-1:123456789012:execution:my-execution-flow' }
+  let(:get_exec_history) { [] }
+
+  before(:each) do
+    allow(Aws::States::Client).to receive(:new).and_return(mock_client)
+    allow(mock_client).to receive(:describe_execution).with(any_args).and_return(desc_exec_resp)
+    allow(mock_client).to receive(:get_execution_history).with(any_args).and_return(get_exec_history)
+  end
+
+  context 'when deploy is running' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'RUNNING') }
+
+    describe 'status' do
+      it 'returns RUNNING' do
+        expect(deployment.status).to eq('RUNNING')
+      end
+    end
+
+    describe 'running?' do
+      it 'returns true' do
+        expect(deployment.running?).to be true
+      end
+    end
+
+    describe 'failure_reason' do
+      it 'should raise an exception' do
+        expect { deployment.failure_reason }.to raise_error(RuntimeError)
+      end
+    end
+  end
+
+  context 'when deploy succeeded' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'SUCCEEDED') }
+
+    describe 'status' do
+      it 'returns SUCCEEDED' do
+        expect(deployment.status).to eq('SUCCEEDED')
+      end
+    end
+
+    describe 'succeeded?' do
+      it 'returns true' do
+        expect(deployment.succeeded?).to be true
+      end
+    end
+
+    describe 'running?' do
+      it 'returns false' do
+        expect(deployment.running?).to be false
+      end
+    end
+
+    describe 'failure_reason' do
+      it 'should raise an exception' do
+        expect { deployment.failure_reason }.to raise_error(RuntimeError)
+      end
+    end
+  end
+
+  context 'when deploy failed' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'FAILED') }
+
+    describe 'status' do
+      it 'returns FAILED' do
+        expect(deployment.status).to eq('FAILED')
+      end
+    end
+
+    describe 'failed?' do
+      it 'returns true' do
+        expect(deployment.failed?).to be true
+      end
+    end
+
+    describe 'running?' do
+      it 'returns false' do
+        expect(deployment.running?).to be false
+      end
+    end
+  end
+
+  context 'when deploy has been aborted' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'ABORTED') }
+
+    describe 'status' do
+      it 'returns ABORTED' do
+        expect(deployment.status).to eq('ABORTED')
+      end
+    end
+
+    describe 'aborted?' do
+      it 'returns true' do
+        expect(deployment.aborted?).to be true
+      end
+    end
+
+    describe 'running?' do
+      it 'returns false' do
+        expect(deployment.running?).to be false
+      end
+    end
+  end
+
+  context 'when deploy has timed out' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'TIMED_OUT') }
+
+    describe 'status' do
+      it 'returns TIMED_OUT' do
+        expect(deployment.status).to eq('TIMED_OUT')
+      end
+    end
+
+    describe 'timed_out?' do
+      it 'returns true' do
+        expect(deployment.timed_out?).to be true
+      end
+    end
+
+    describe 'running?' do
+      it 'returns false' do
+        expect(deployment.running?).to be false
+      end
+    end
+  end
+
+  context 'when deploy has failed' do
+    let(:desc_exec_resp) { Aws::States::Types::DescribeExecutionOutput.new(status: 'FAILED') }
+
+    describe 'status' do
+      it 'returns FAILED' do
+        expect(deployment.status).to eq('FAILED')
+      end
+    end
+
+    describe 'failed?' do
+      it 'returns true' do
+        expect(deployment.failed?).to be true
+      end
+    end
+
+    describe 'running?' do
+      it 'returns false' do
+        expect(deployment.running?).to be false
+      end
+    end
+
+    context 'when due to LambdaFunctionFailed event' do
+      let(:get_exec_history) do
+        Aws::States::Types::GetExecutionHistoryOutput.new(
+          events: [
+            '',
+            Aws::States::Types::HistoryEvent.new(type: 'LambdaFunctionFailed')
+          ]
+        )
+      end
+
+      describe 'failure_reason' do
+        it 'calls LambdaFunctionFailedError.new(fail_event).error' do
+          expect_any_instance_of(Deployment::Events::LambdaFunctionFailed).to receive(:error)
+          subject.failure_reason
+        end
+      end
+    end
+
+    context 'when due to FailStateEntered event' do
+      let(:get_exec_history) do
+        Aws::States::Types::GetExecutionHistoryOutput.new(
+          events: [
+            '',
+            Aws::States::Types::HistoryEvent.new(type: 'FailStateEntered')
+          ]
+        )
+      end
+
+      describe 'failure_reason' do
+        it 'calls FailStateEntered.new(fail_event).error' do
+          expect_any_instance_of(Deployment::Events::FailStateEntered).to receive(:error)
+          subject.failure_reason
+        end
+      end
+    end
+
+    context 'when due to and unknown event' do
+      let(:get_exec_history) do
+        Aws::States::Types::GetExecutionHistoryOutput.new(
+          events: [
+            '',
+            Aws::States::Types::HistoryEvent.new(type: 'UnknownError')
+          ]
+        )
+      end
+
+      describe 'failure_reason' do
+        it 'returns a generic error message' do
+          expect(subject.failure_reason).to start_with('Uncaught failure.')
+        end
+      end
+    end
+  end
+end
diff --git a/spec/fail_state_entered_spec.rb b/spec/fail_state_entered_spec.rb
new file mode 100644
index 0000000..d9aa4f3
--- /dev/null
+++ b/spec/fail_state_entered_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Deployment::Events::FailStateEntered do
+  subject(:deployment) { Deployment::Events::FailStateEntered.new(event, execution_arn) }
+
+  let(:execution_arn) { 'arn:aws:states:eu-west-1:123456789012:execution:my-execution-flow' }
+
+  context 'when Sidekiq has failed to start' do
+    let(:event) do
+      Aws::States::Types::HistoryEvent.new(
+        type: 'FailStateEntered',
+        state_entered_event_details: Aws::States::Types::StateEnteredEventDetails.new(
+          input: '
+                {
+                  "Error": {
+                    "Cause":"{\"errorMessage\":\"ECS deployment status: IN_PROGRESS\",\"errorType\":\"Function<DeployInProgress>\",\"stackTrace\":[\"/var/task/ecs_deployment_handler.rb:49:in `handler\"]}",
+                    "error":"Function<DeployInProgress>",
+                    "resource":"invoke",
+                    "resourceType":"lambda"
+                  }
+                }
+              '
+        )
+      )
+    end
+
+    describe(:error) do
+      it 'returns the correct error message' do
+        expect(deployment.error).to eq('Sidekiq workers failed to start or failed to stabilise.')
+      end
+    end
+  end
+
+  context 'when there is some other failure' do
+    let(:event) do
+      Aws::States::Types::HistoryEvent.new(
+        type: 'FailStateEntered',
+        state_entered_event_details: Aws::States::Types::StateEnteredEventDetails.new(
+          input: '
+                {
+                  "Error": {
+                    "Cause":"{\"errorMessage\":\"Some other error\"}",
+                    "error":"Function<DeployInProgress>",
+                    "resource":"invoke",
+                    "resourceType":"lambda"
+                  }
+                }
+              '
+        )
+      )
+    end
+
+    describe(:error) do
+      it 'returns the error message' do
+        expect(deployment.error).to start_with('Failure message: Some other error')
+      end
+    end
+  end
+end
diff --git a/spec/lambda_function_failed_spec.rb b/spec/lambda_function_failed_spec.rb
new file mode 100644
index 0000000..d17fb08
--- /dev/null
+++ b/spec/lambda_function_failed_spec.rb
@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Deployment::Events::LambdaFunctionFailed do
+  subject(:deployment) { Deployment::Events::LambdaFunctionFailed.new(event) }
+
+  context 'forward deploy pre-flight check failed' do
+    let(:event) do
+      Aws::States::Types::HistoryEvent.new(
+        type: 'LambdaFunctionFailed',
+        lambda_function_failed_event_details: Aws::States::Types::LambdaFunctionFailedEventDetails.new(
+          cause: '
+            {
+              "errorMessage": "Pre flight checks failed:\n{\"Checks\"=>{:RequiredParameters=>\"PASSED\", :CommitCheck=>\"PASSED\", :ScheduleCheck=>\"PASSED\", :ForwardDeployCheck=>\"FAILED\"}, \"Status\"=>\"FAILED\"}",
+              "errorType": "Function<StandardError>",
+              "stackTrace": [
+                "/var/task/pre_flight_checks.rb:145:in `handler"
+              ]
+            }'
+        )
+      )
+    end
+
+    describe(:error) do
+      it 'returns the correct error message' do
+        expect(deployment.error).to start_with('Forward deploy check FAILED.')
+      end
+    end
+  end
+
+  context 'some other pre-flight check failed' do
+    let(:event) do
+      Aws::States::Types::HistoryEvent.new(
+        type: 'LambdaFunctionFailed',
+        lambda_function_failed_event_details: Aws::States::Types::LambdaFunctionFailedEventDetails.new(
+          cause: '
+            {
+              "errorMessage": "Pre flight checks failed:\n{\"Checks\"=>{:RequiredParameters=>\"FAILED\", :CommitCheck=>\"PASSED\", :ScheduleCheck=>\"PASSED\", :ForwardDeployCheck=>\"PASSED\"}, \"Status\"=>\"FAILED\"}",
+              "errorType": "Function<StandardError>",
+              "stackTrace": [
+                "/var/task/pre_flight_checks.rb:145:in `handler"
+              ]
+            }'
+        )
+      )
+    end
+
+    describe(:error) do
+      it 'returns a generic Pre flight checks failed error message' do
+        expect(deployment.error).to start_with('Pre flight checks failed:')
+      end
+    end
+  end
+
+  context 'some other function failed' do
+    let(:event) do
+      Aws::States::Types::HistoryEvent.new(
+        type: 'LambdaFunctionFailed',
+        lambda_function_failed_event_details: Aws::States::Types::LambdaFunctionFailedEventDetails.new(
+          cause: '
+            {
+              "errorMessage": "Some other error",
+              "errorType": "Function<StandardError>",
+              "stackTrace": [
+                "/var/task/another_function.rb:145:in `handler"
+              ]
+            }'
+        )
+      )
+    end
+
+    describe(:error) do
+      it 'returns the error message' do
+        expect(deployment.error).to start_with('Some other error')
+      end
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..b4ce74d
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,3 @@
+$LOAD_PATH.unshift File.expand_path('../', 'lib')
+require 'deployment'
+require 'aws-sdk-states'