Add a test for removing runners

- When cleaning up runners after tests finish, ignore runners if
they've already been removed

qa/qa/resource/runner.rb

@@ -47,9 +47,8 @@ module QA
 
       def remove_via_api!
         runners = project.runners(tag_list: @tags)
-        unless runners && !runners.empty?
-          raise "Project #{project.path_with_namespace} has no runners#{" with tags #{@tags}." if @tags&.any?}"
-        end
+
+        return if runners.blank?
 
         this_runner = runners.find { |runner| runner[:description] == name }
         unless this_runner

qa/qa/specs/features/api/4_verify/remove_runner_spec.rb

+# frozen_string_literal: true
+
+module QA
+  RSpec.describe 'Verify', :runner do
+    describe 'Runner removal' do
+      include Support::API
+
+      let(:api_client) { Runtime::API::Client.new(:gitlab) }
+      let(:executor) { "qa-runner-#{Time.now.to_i}" }
+      let(:runner_tags) { ['runner-registration-e2e-test'] }
+      let!(:runner) do
+        Resource::Runner.fabricate! do |runner|
+          runner.name = executor
+          runner.tags = runner_tags
+        end
+      end
+
+      before do
+        sleep 5 # Runner should register within 5 seconds
+      end
+
+      # Removing a runner via the UI is covered by `spec/features/runners_spec.rb``
+      it 'removes the runner' do
+        expect(runner.project.runners.size).to eq(1)
+        expect(runner.project.runners.first[:description]).to eq(executor)
+
+        request = Runtime::API::Request.new(api_client, "runners/#{runner.project.runners.first[:id]}")
+        response = delete(request.url)
+        expect(response.code).to eq(Support::API::HTTP_STATUS_NO_CONTENT)
+        expect(response.body).to be_empty
+
+        expect(runner.project.runners).to be_empty
+      end
+    end
+  end
+end