Add task for deleting a user

Adds a new task for deleting an individual user, and a dry run task for
checking it in advance.

Doesn't delete any associated forms or groups - this complicates things
quite a lot and it's less risky for live forms if we delete or reassign
those form/group associations prior to running this task to delete the
user.

lib/tasks/users.rake

@@ -12,6 +12,18 @@ namespace :users do
   task update_user_roles_to_standard: :environment do
     update_user_roles
   end
+
+  desc "Delete user (dry run)"
+  task :delete_user_dry_run, %i[user_id] => :environment do |_, args|
+    run_deletion_task("delete_user_dry_run", args, rollback: true)
+  end
+
+  desc "Delete user"
+  task :delete_user, %i[user_id] => :environment do |_, args|
+    # This task doesn't check whether the user is associated with any forms or groups.
+    # Before running the task, remove the user from any groups and reassign their forms to another user.
+    run_deletion_task("delete_user", args, rollback: false)
+  end
 end
 
 def update_user_roles
@@ -29,3 +41,16 @@ def update_user_roles
   Rails.logger.info("Number of organisation_admin users: #{User.where(role: 'organisation_admin').count}")
   Rails.logger.info("Number of super_admin users: #{User.where(role: 'super_admin').count}")
 end
+
+def run_deletion_task(task_name, args, rollback:)
+  usage_message = "usage: rake #{task_name}[<user_id>]".freeze
+  abort usage_message if args[:user_id].blank?
+
+  ActiveRecord::Base.transaction do
+    user = User.find(args[:user_id])
+    user.destroy!
+    Rails.logger.info("Deleted user: #{args[:user_id]}")
+    Rails.logger.info("users:delete_user_dry_run: rollback deletion of user #{args[:user_id]}") if rollback
+    raise ActiveRecord::Rollback if rollback
+  end
+end

spec/lib/tasks/users.rake_spec.rb

@@ -29,4 +29,71 @@
       expect(org_admin_user.reload.role).to eq("organisation_admin")
     end
   end
+
+  describe "users:delete_user_dry_run" do
+    subject(:task) do
+      Rake::Task["users:delete_user_dry_run"]
+        .tap(&:reenable) # make sure task is invoked every time
+    end
+
+    let!(:user_to_delete) { create(:user) }
+
+    context "when a user ID is provided" do
+      it "does not delete the user" do
+        expect {
+          task.invoke(user_to_delete.id)
+
+          user_to_delete.reload
+        }.not_to raise_error(ActiveRecord::RecordNotFound)
+      end
+
+      it "logs the deletion and the rollback" do
+        expect(Rails.logger).to receive(:info).with("Deleted user: #{user_to_delete.id}")
+        expect(Rails.logger).to receive(:info).with("users:delete_user_dry_run: rollback deletion of user #{user_to_delete.id}")
+        task.invoke(user_to_delete.id)
+      end
+    end
+
+    context "when a user ID is not provided" do
+      it "aborts with a usage message" do
+        expect {
+          task.invoke
+        }.to raise_error(SystemExit)
+        .and output("usage: rake delete_user_dry_run[<user_id>]\n").to_stderr
+      end
+    end
+  end
+
+  describe "users:delete_user" do
+    subject(:task) do
+      Rake::Task["users:delete_user"]
+        .tap(&:reenable) # make sure task is invoked every time
+    end
+
+    let!(:user_to_delete) { create(:user) }
+
+    context "when a user ID is provided" do
+      it "deletes the user" do
+        expect {
+          task.invoke(user_to_delete.id)
+
+          user_to_delete.reload
+        }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+
+      it "logs the deletion" do
+        expect(Rails.logger).to receive(:info).with("Deleted user: #{user_to_delete.id}")
+        task.invoke(user_to_delete.id)
+      end
+    end
+
+    context "when a user ID is not provided" do
+      it "aborts with a usage message" do
+        expect {
+          task.invoke
+        }.to raise_error(SystemExit)
+        .and output("usage: rake delete_user[<user_id>]\n").to_stderr
+      end
+    end
+  end
 end