diff --git a/app/concepts/project/operation/update.rb b/app/concepts/project/operation/update.rb
new file mode 100644
index 000000000..d210d321f
--- /dev/null
+++ b/app/concepts/project/operation/update.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+class Project
+  module Operation
+    class Update
+      require 'operation_response'
+
+      def self.call(params, project)
+        response = setup_response(project)
+
+        setup_deletions(response, params)
+        update_project_attributes(response, params)
+        update_component_attributes(response, params)
+        persist_changes(response)
+
+        response
+      end
+
+      class << self
+        private
+
+        def setup_response(project)
+          response = OperationResponse.new
+          response[:project] = project
+          response
+        end
+
+        def setup_deletions(response, params)
+          existing_component_ids = response[:project].components.pluck(:id)
+          updated_component_ids = params[:components].pluck(:id)
+          response[:component_ids_to_delete] = existing_component_ids - updated_component_ids
+
+          validate_deletions(response)
+        end
+
+        def validate_deletions(response)
+          default_component_id = response[:project].components.find_by(default: true)&.id
+          return unless response[:component_ids_to_delete]&.include?(default_component_id)
+
+          response[:error] = I18n.t 'errors.project.editing.delete_default_component'
+        end
+
+        def update_project_attributes(response, params)
+          return if response[:error]
+
+          response[:project].assign_attributes(params.slice(:name))
+        end
+
+        def update_component_attributes(response, params)
+          return if response[:error]
+
+          params[:components].each do |component_params|
+            if component_params[:id].present?
+              component = response[:project].components.select { |c| c.id == component_params[:id] }.first
+              component.assign_attributes(component_params)
+            else
+              response[:project].components.build(component_params)
+            end
+          end
+        end
+
+        def persist_changes(response)
+          return if response[:error]
+
+          ActiveRecord::Base.transaction do
+            response[:project].save!
+            response[:project].components.where(id: response[:component_ids_to_delete]).destroy_all
+          rescue StandardError
+            # TODO: log error?
+            response[:error] = 'Error persisting changes'
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/app/controllers/api/projects_controller.rb b/app/controllers/api/projects_controller.rb
index f773d8b66..0de3c02c5 100644
--- a/app/controllers/api/projects_controller.rb
+++ b/app/controllers/api/projects_controller.rb
@@ -3,33 +3,34 @@
 module Api
   class ProjectsController < ApiController
     require 'phrase_identifier'
-
     before_action :require_oauth_user, only: %i[update]
+    before_action :load_project
+    load_and_authorize_resource
 
     def show
-      @project = Project.find_by!(identifier: params[:id])
       render :show, formats: [:json]
     end
 
     def update
-      @project = Project.find_by!(identifier: params[:id])
-      authorize! :update, @project
+      result = Project::Operation::Update.call(project_params, @project)
 
-      components = project_params[:components]
-      components.each do |comp_params|
-        component = Component.find(comp_params[:id])
-        component.update(comp_params)
+      if result.success?
+        render :show, formats: [:json]
+      else
+        render json: { error: result[:error] }, status: :bad_request
       end
-      head :ok
     end
 
     private
 
+    def load_project
+      @project = Project.find_by!(identifier: params[:id])
+    end
+
     def project_params
       params.require(:project)
-            .permit(:identifier,
-                    :type,
-                    components: %i[id name extension content])
+            .permit(:name,
+                    components: %i[id name extension content index])
     end
   end
 end
diff --git a/app/models/ability.rb b/app/models/ability.rb
index 438d12901..fa724636c 100644
--- a/app/models/ability.rb
+++ b/app/models/ability.rb
@@ -4,6 +4,8 @@ class Ability
   include CanCan::Ability
 
   def initialize(user)
+    can :read, Project
+
     return if user.blank?
 
     can :update, Project, user_id: user
diff --git a/app/models/component.rb b/app/models/component.rb
index f8b53364f..eb8eb2dc8 100644
--- a/app/models/component.rb
+++ b/app/models/component.rb
@@ -2,4 +2,17 @@
 
 class Component < ApplicationRecord
   belongs_to :project
+  validates :name, presence: true
+  validates :extension, presence: true
+  validates :index, presence: true, uniqueness: { scope: :project_id }
+  validate :default_component_protected_properties, on: :update
+
+  private
+
+  def default_component_protected_properties
+    return unless default?
+
+    errors.add(:name, I18n.t('errors.project.editing.change_default_name')) if name_changed?
+    errors.add(:extension, I18n.t('errors.project.editing.change_default_extension')) if extension_changed?
+  end
 end
diff --git a/app/models/project.rb b/app/models/project.rb
index 8830427c6..094d3c7d5 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -8,6 +8,7 @@ class Project < ApplicationRecord
   belongs_to :parent, class_name: 'Project', foreign_key: 'remixed_from_id', optional: true, inverse_of: :children
   has_many :components, -> { order(:index) }, dependent: :destroy, inverse_of: :project
   has_many :children, class_name: 'Project', foreign_key: 'remixed_from_id', dependent: :nullify, inverse_of: :parent
+  accepts_nested_attributes_for :components
 
   private
 
diff --git a/app/views/api/projects/show.json.jbuilder b/app/views/api/projects/show.json.jbuilder
index a3929b9af..da085ad97 100644
--- a/app/views/api/projects/show.json.jbuilder
+++ b/app/views/api/projects/show.json.jbuilder
@@ -4,4 +4,4 @@ json.call(@project, :identifier, :project_type, :name, :user_id)
 
 json.parent(@project.parent, :name, :identifier) if @project.parent
 
-json.components @project.components, :id, :name, :extension, :content
+json.components @project.components, :id, :name, :extension, :content, :index
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8ca56fc74..d5379a51c 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1,33 +1,7 @@
-# Files in the config/locales directory are used for internationalization
-# and are automatically loaded by Rails. If you want to use locales other
-# than English, add the necessary files in this directory.
-#
-# To use the locales, use `I18n.t`:
-#
-#     I18n.t "hello"
-#
-# In views, this is aliased to just `t`:
-#
-#     <%= t("hello") %>
-#
-# To use a different locale, set it with `I18n.locale`:
-#
-#     I18n.locale = :es
-#
-# This would use the information in config/locales/es.yml.
-#
-# The following keys must be escaped otherwise they will not be retrieved by
-# the default I18n backend:
-#
-# true, false, on, off, yes, no
-#
-# Instead, surround them with single quotes.
-#
-# en:
-#   "true": "foo"
-#
-# To learn more, please read the Rails Internationalization guide
-# available at https://guides.rubyonrails.org/i18n.html.
-
 en:
-  hello: "Hello world"
+  errors:
+    project:
+      editing:
+        delete_default_component: 'Cannot delete default file'
+        change_default_name: 'Cannot amend default file name'
+        change_default_extension: 'Cannot amend default file extension'
diff --git a/config/routes.rb b/config/routes.rb
index 0b07b8978..aa0d8afc9 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1,11 +1,6 @@
 # frozen_string_literal: true
 
 Rails.application.routes.draw do
-  # Define your application routes per the DSL in https://guides.rubyonrails.org/routing.html
-
-  # Defines the root path route ("/")
-  # root "articles#index"
-
   namespace :api do
     resource :default_project, only: %i[show create] do
       get '/html', to: 'default_projects#html'
diff --git a/db/migrate/20220307144811_allow_nil_content_on_components.rb b/db/migrate/20220307144811_allow_nil_content_on_components.rb
new file mode 100644
index 000000000..b1a233764
--- /dev/null
+++ b/db/migrate/20220307144811_allow_nil_content_on_components.rb
@@ -0,0 +1,9 @@
+class AllowNilContentOnComponents < ActiveRecord::Migration[7.0]
+  def up
+    change_column :components, :content, :string, null: true
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end
diff --git a/db/migrate/20220308115005_add_default_flag_to_components.rb b/db/migrate/20220308115005_add_default_flag_to_components.rb
new file mode 100644
index 000000000..9a2dce29d
--- /dev/null
+++ b/db/migrate/20220308115005_add_default_flag_to_components.rb
@@ -0,0 +1,5 @@
+class AddDefaultFlagToComponents < ActiveRecord::Migration[7.0]
+  def change
+    add_column :components, :default, :boolean, null: false, default: false
+  end
+end
diff --git a/db/migrate/20220310120419_add_unique_index_components.rb b/db/migrate/20220310120419_add_unique_index_components.rb
new file mode 100644
index 000000000..78d958ec0
--- /dev/null
+++ b/db/migrate/20220310120419_add_unique_index_components.rb
@@ -0,0 +1,5 @@
+class AddUniqueIndexComponents < ActiveRecord::Migration[7.0]
+  def change
+    add_index :components, [:index, :project_id], unique: true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 7ebc5b8a1..8d5dbec3b 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2022_02_28_094815) do
+ActiveRecord::Schema.define(version: 2022_03_10_120419) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
@@ -20,10 +20,12 @@
     t.uuid "project_id"
     t.string "name", null: false
     t.string "extension", null: false
-    t.text "content", null: false
+    t.string "content"
     t.datetime "created_at", precision: 6, null: false
     t.datetime "updated_at", precision: 6, null: false
     t.integer "index"
+    t.boolean "default", default: false, null: false
+    t.index ["index", "project_id"], name: "index_components_on_index_and_project_id", unique: true
     t.index ["project_id"], name: "index_components_on_project_id"
   end
 
diff --git a/lib/tasks/project_components/hello_world_example/project_config.yml b/lib/tasks/project_components/hello_world_example/project_config.yml
index 0d29c4267..0fa21cbad 100644
--- a/lib/tasks/project_components/hello_world_example/project_config.yml
+++ b/lib/tasks/project_components/hello_world_example/project_config.yml
@@ -5,11 +5,14 @@ COMPONENTS:
     extension: "py"
     location: "main.py"
     index: 0
+    default: true
   - name: "emoji"
     extension: "py"
     location: "emoji.py"
     index: 1
+    default: false
   - name: "noemoji"
     extension: "py"
     location: "noemoji.py"
-    index: 2
\ No newline at end of file
+    index: 2
+    default: false
diff --git a/lib/tasks/project_components/hello_world_starter/project_config.yml b/lib/tasks/project_components/hello_world_starter/project_config.yml
index 8e1bc82ce..ae1bd5a8d 100644
--- a/lib/tasks/project_components/hello_world_starter/project_config.yml
+++ b/lib/tasks/project_components/hello_world_starter/project_config.yml
@@ -5,11 +5,14 @@ COMPONENTS:
     extension: "py"
     location: "main.py"
     index: 0
+    default: true
   - name: "emoji"
     extension: "py"
     location: "emoji.py"
     index: 1
+    default: false
   - name: "noemoji"
     extension: "py"
     location: "noemoji.py"
-    index: 2
\ No newline at end of file
+    index: 2
+    default: false
diff --git a/lib/tasks/project_components/target_practice_example/project_config.yml b/lib/tasks/project_components/target_practice_example/project_config.yml
index b221ea73c..3fbd1fd5d 100644
--- a/lib/tasks/project_components/target_practice_example/project_config.yml
+++ b/lib/tasks/project_components/target_practice_example/project_config.yml
@@ -4,4 +4,5 @@ COMPONENTS:
   - name: "main"
     extension: "py"
     location: "main.py"
-    index: 0
\ No newline at end of file
+    index: 0
+    default: true
diff --git a/lib/tasks/project_components/target_practice_starter/project_config.yml b/lib/tasks/project_components/target_practice_starter/project_config.yml
index 12de0e7f3..0ea0f287b 100644
--- a/lib/tasks/project_components/target_practice_starter/project_config.yml
+++ b/lib/tasks/project_components/target_practice_starter/project_config.yml
@@ -4,4 +4,5 @@ COMPONENTS:
   - name: "main"
     extension: "py"
     location: "main.py"
-    index: 0
\ No newline at end of file
+    index: 0
+    default: true
diff --git a/lib/tasks/projects.rake b/lib/tasks/projects.rake
index 0e17816ff..3a5e7d33c 100644
--- a/lib/tasks/projects.rake
+++ b/lib/tasks/projects.rake
@@ -15,7 +15,9 @@ namespace :projects do
         extension = component['extension']
         code = File.read(File.dirname(__FILE__) + "/project_components/#{dir}/#{component['location']}")
         index = component['index']
-        project_component = Component.new(name: name, extension: extension, content: code, index: index)
+        default = component['default']
+        project_component = Component.new(name: name, extension: extension, content: code, index: index,
+                                          default: default)
         new_project.components << project_component
       end
       new_project.save
diff --git a/spec/concepts/project/operation/update_default_component_spec.rb b/spec/concepts/project/operation/update_default_component_spec.rb
new file mode 100644
index 000000000..7d888c323
--- /dev/null
+++ b/spec/concepts/project/operation/update_default_component_spec.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Project::Operation::Update, type: :unit do
+  subject(:update) { described_class.call(project_params, project) }
+
+  let!(:project) { create(:project, :with_default_component) }
+  let(:default_component) { project.components.first }
+
+  describe '.call' do
+    context 'when default file is removed' do
+      let(:project_params) do
+        {
+          name: 'updated project name',
+          components: []
+        }
+      end
+
+      it 'returns failure? true' do
+        expect(update.failure?).to eq(true)
+      end
+
+      it 'returns error message' do
+        expect(update[:error]).to eq(I18n.t('errors.project.editing.delete_default_component'))
+      end
+
+      it 'does not delete the default component' do
+        expect { update }.not_to change(Component, :count)
+      end
+
+      it 'does not update project' do
+        expect { update }.not_to change { project.reload.name }
+      end
+    end
+
+    context 'when default file properties are changed' do
+      let(:default_component_params) do
+        default_component.attributes.symbolize_keys.slice(
+          :id,
+          :name,
+          :content,
+          :extension,
+          :index
+        )
+      end
+
+      let(:project_params) do
+        {
+          name: 'updated project name',
+          components: [default_component_params]
+        }
+      end
+
+      it 'does not update file name' do
+        default_component_params[:name] = 'Updated name'
+        expect { update }.not_to change { default_component.reload.name }
+      end
+
+      it 'does not update file extension' do
+        default_component_params[:extension] = 'txt'
+        expect { update }.not_to change { default_component.reload.extension }
+      end
+
+      it 'does not update project' do
+        default_component_params[:name] = 'Updated name'
+        expect { update }.not_to change { project.reload.name }
+      end
+    end
+  end
+end
diff --git a/spec/concepts/project/operation/update_delete_components_spec.rb b/spec/concepts/project/operation/update_delete_components_spec.rb
new file mode 100644
index 000000000..b33ec43d7
--- /dev/null
+++ b/spec/concepts/project/operation/update_delete_components_spec.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Project::Operation::Update, type: :unit do
+  subject(:update) { described_class.call(project_params, project) }
+
+  let!(:project) { create(:project, :with_default_component, :with_components) }
+  let(:component_to_delete) { project.components.last }
+  let(:default_component) { project.components.first }
+
+  let(:default_component_params) do
+    default_component.attributes.symbolize_keys.slice(
+      :id,
+      :name,
+      :content,
+      :extension,
+      :index
+    )
+  end
+
+  describe '.call' do
+    context 'when an existing component has been removed' do
+      let(:project_params) do
+        {
+          name: 'updated project name',
+          components: [default_component_params]
+        }
+      end
+
+      it 'deletes a component' do
+        expect { update }.to change(Component, :count).by(-1)
+      end
+
+      it 'deletes the correct component' do
+        update
+        expect(Component.find_by(id: component_to_delete.id)).to eq(nil)
+      end
+    end
+  end
+end
diff --git a/spec/concepts/project/operation/update_invalid_spec.rb b/spec/concepts/project/operation/update_invalid_spec.rb
new file mode 100644
index 000000000..2725c1fac
--- /dev/null
+++ b/spec/concepts/project/operation/update_invalid_spec.rb
@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Project::Operation::Update, type: :unit do
+  subject(:update) do
+    params = {
+      name: 'updated project name',
+      components: [default_component_params, edited_component_params, new_component_params]
+    }
+    described_class.call(params, project)
+  end
+
+  let!(:project) { create(:project, :with_default_component, :with_components, component_count: 2) }
+  let(:editable_component) { project.components.last }
+  let(:default_component) { project.components.first }
+
+  let(:edited_component_params) do
+    {
+      id: editable_component.id,
+      name: nil,
+      content: 'updated content',
+      extension: 'py',
+      index: 5
+    }
+  end
+
+  describe '.call' do
+    context 'when updated project component is invalid' do
+      it 'returns failure? true' do
+        expect(update.failure?).to eq(true)
+      end
+
+      it 'does not amend any project properties' do
+        expect { update }.not_to change { project.reload.name }
+      end
+
+      it 'does not amend any component properties' do
+        expect { update }.not_to change { component_properties_hash(editable_component.reload) }
+      end
+
+      it 'does not create or delete components' do
+        expect { update }.not_to change(Component, :count)
+      end
+    end
+  end
+
+  def component_properties_hash(component)
+    component.attributes.symbolize_keys.slice(:name, :content, :extension, :index)
+  end
+
+  def default_component_params
+    default_component.attributes.symbolize_keys.slice(
+      :id,
+      :name,
+      :content,
+      :extension,
+      :index
+    )
+  end
+
+  def new_component_params
+    {
+      name: 'new component',
+      content: 'new component content',
+      extension: 'py',
+      index: 99
+    }
+  end
+end
diff --git a/spec/concepts/project/operation/update_spec.rb b/spec/concepts/project/operation/update_spec.rb
new file mode 100644
index 000000000..e815ccdd2
--- /dev/null
+++ b/spec/concepts/project/operation/update_spec.rb
@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Project::Operation::Update, type: :unit do
+  subject(:update) do
+    params = {
+      name: 'updated project name',
+      components: component_params
+    }
+    described_class.call(params, project)
+  end
+
+  let!(:project) { create(:project, :with_default_component, :with_components) }
+  let(:editable_component) { project.components.last }
+  let(:default_component) { project.components.first }
+
+  describe '.call' do
+    let(:edited_component_params) do
+      {
+        id: editable_component.id,
+        name: 'updated component name',
+        content: 'updated content',
+        extension: 'py',
+        index: 5
+      }
+    end
+
+    context 'when only amending components' do
+      let(:component_params) { [default_component_params, edited_component_params] }
+
+      it 'returns success? true' do
+        expect(update.success?).to eq(true)
+      end
+
+      it 'updates project properties' do
+        expect { update }.to change { project.reload.name }.to('updated project name')
+      end
+
+      it 'updates component properties' do
+        expect { update }
+          .to change { component_properties_hash(editable_component.reload) }
+          .to(edited_component_params.slice(:name, :content, :extension, :index))
+      end
+    end
+
+    context 'when a new component has been added' do
+      let(:component_params) { [default_component_params, edited_component_params, new_component_params] }
+
+      it 'creates a new component' do
+        expect { update }.to change(Component, :count).by(1)
+      end
+
+      it 'creates component with correct properties' do
+        update
+        created_component = project.components.find_by(**new_component_params)
+        expect(created_component).not_to eq(nil)
+      end
+    end
+  end
+
+  def component_properties_hash(component)
+    component.attributes.symbolize_keys.slice(:name, :content, :extension, :index)
+  end
+
+  def default_component_params
+    default_component.attributes.symbolize_keys.slice(
+      :id,
+      :name,
+      :content,
+      :extension,
+      :index
+    )
+  end
+
+  def new_component_params
+    {
+      name: 'new component',
+      content: 'new component content',
+      extension: 'py',
+      index: 99
+    }
+  end
+end
diff --git a/spec/factories/component.rb b/spec/factories/component.rb
index 74c43dba1..20b3b7841 100644
--- a/spec/factories/component.rb
+++ b/spec/factories/component.rb
@@ -4,6 +4,14 @@
   factory :component do
     name { Faker::Lorem.word }
     extension { 'py' }
-    content { Faker::Lorem.paragraph(sentence_count: 2) }
+    sequence(:index) { |n| n }
+    default { false }
+    project
+
+    factory :default_python_component do
+      name { 'main' }
+      index { 0 }
+      default { true }
+    end
   end
 end
diff --git a/spec/factories/project.rb b/spec/factories/project.rb
index 7badbdcb8..fbcc39fd1 100644
--- a/spec/factories/project.rb
+++ b/spec/factories/project.rb
@@ -8,8 +8,20 @@
     project_type { 'python' }
 
     trait :with_components do
+      transient do
+        component_count { 1 }
+      end
+
+      after(:create) do |object, evaluator|
+        object.components << FactoryBot.create_list(:component,
+                                                    evaluator.component_count,
+                                                    project: object)
+      end
+    end
+
+    trait :with_default_component do
       after(:create) do |object|
-        object.components = FactoryBot.create_list(:component, 2, project: object)
+        object.components << FactoryBot.create(:default_python_component, project: object)
       end
     end
   end
diff --git a/spec/models/component_spec.rb b/spec/models/component_spec.rb
index b041ddad8..9fd7812d9 100644
--- a/spec/models/component_spec.rb
+++ b/spec/models/component_spec.rb
@@ -3,5 +3,41 @@
 require 'rails_helper'
 
 RSpec.describe Component, type: :model do
+  subject { build(:component) }
+
   it { is_expected.to belong_to(:project) }
+  it { is_expected.to validate_presence_of(:name) }
+  it { is_expected.to validate_presence_of(:extension) }
+  it { is_expected.to validate_presence_of(:index) }
+  it { is_expected.to validate_uniqueness_of(:index).scoped_to(:project_id) }
+
+  context 'when default component' do
+    let(:component) { create(:default_python_component) }
+
+    describe 'validations' do
+      it 'returns valid? false when name changed' do
+        component.name = 'updated'
+        expect(component.valid?).to eq(false)
+      end
+
+      it 'sets error message when name changed' do
+        component.name = 'updated'
+        component.valid?
+        expect(component.errors[:name])
+          .to include(I18n.t('errors.project.editing.change_default_name'))
+      end
+
+      it 'returns valid? false when extension changed' do
+        component.extension = 'txt'
+        expect(component.valid?).to eq(false)
+      end
+
+      it 'sets error message when extension changed' do
+        component.extension = 'txt'
+        component.valid?
+        expect(component.errors[:extension])
+          .to include(I18n.t('errors.project.editing.change_default_extension'))
+      end
+    end
+  end
 end
diff --git a/spec/request/projects/update_spec.rb b/spec/request/projects/update_spec.rb
index 0c97d046e..dcaaa422f 100644
--- a/spec/request/projects/update_spec.rb
+++ b/spec/request/projects/update_spec.rb
@@ -1,16 +1,32 @@
 # frozen_string_literal: true
 
 require 'rails_helper'
+require_relative '../../../lib/operation_response'
 
 RSpec.describe 'Project update requests', type: :request do
   let(:user_id) { 'e0675b6c-dc48-4cd6-8c04-0f7ac05af51a' }
   let(:project) { create(:project, user_id: user_id) }
 
   context 'when authed user is project creator' do
-    let(:project) { create(:project, user_id: user_id) }
+    let(:project) { create(:project, :with_default_component, user_id: user_id) }
     let!(:component) { create(:component, project: project) }
-    let(:changes) { { name: 'updated', extension: 'py', content: 'updated content' } }
-    let(:params) { { project: { components: [{ id: component.id, **changes }] } } }
+    let(:default_component_params) do
+      project.components.first.attributes.symbolize_keys.slice(
+        :id,
+        :name,
+        :content,
+        :extension,
+        :index
+      )
+    end
+
+    let(:params) do
+      { project:
+        { components: [
+          default_component_params,
+          { id: component.id, name: 'updated', extension: 'py', content: 'updated component content' }
+        ] } }
+    end
 
     before do
       mock_oauth_user(user_id)
@@ -21,10 +37,26 @@
       expect(response.status).to eq(200)
     end
 
-    it 'updates component' do
+    it 'returns updated project json' do
       put "/api/projects/#{project.identifier}", params: params
-      updated = component.reload.attributes.symbolize_keys.slice(:name, :content, :extension)
-      expect(updated).to eq(changes)
+      expect(response.body).to include('updated component content')
+    end
+
+    it 'calls update operation' do
+      mock_response = instance_double(OperationResponse)
+      allow(mock_response).to receive(:success?).and_return(true)
+      allow(Project::Operation::Update).to receive(:call).and_return(mock_response)
+      put "/api/projects/#{project.identifier}", params: params
+      expect(Project::Operation::Update).to have_received(:call)
+    end
+
+    context 'when update is invalid' do
+      let(:params) { { project: { components: [] } } }
+
+      it 'returns error response' do
+        put "/api/projects/#{project.identifier}", params: params
+        expect(response.status).to eq(400)
+      end
     end
   end
 
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 01f7c9744..5d227ba75 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -70,12 +70,12 @@
   #   # Many RSpec users commonly either run the entire suite or an individual
   #   # file, and it's useful to allow more verbose output when running an
   #   # individual spec file.
-  #   if config.files_to_run.one?
-  #     # Use the documentation formatter for detailed output,
-  #     # unless a formatter has already been configured
-  #     # (e.g. via a command-line flag).
-  #     config.default_formatter = "doc"
-  #   end
+  if config.files_to_run.one?
+    # Use the documentation formatter for detailed output,
+    # unless a formatter has already been configured
+    # (e.g. via a command-line flag).
+    config.default_formatter = 'doc'
+  end
   #
   #   # Print the 10 slowest examples and example groups at the
   #   # end of the spec run, to help surface which specs are running