Add spec for alert status mutation

spec/requests/api/graphql/mutations/alert_management/alerts/update_alert_status_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Setting the status of an alert' do
+  include GraphqlHelpers
+
+  let_it_be(:user) { create(:user) }
+  let_it_be(:project) { create(:project) }
+  let(:alert) { create(:alert_management_alert, project: project) }
+  let(:input) { { status: 'ACKNOWLEDGED' } }
+
+  let(:mutation) do
+    variables = {
+      project_path: project.full_path,
+      iid: alert.iid.to_s
+    }
+    graphql_mutation(:update_alert_status, variables.merge(input),
+                     <<~QL
+                       clientMutationId
+                       errors
+                       alert {
+                         iid
+                         status
+                       }
+                     QL
+    )
+  end
+
+  let(:mutation_response) { graphql_mutation_response(:update_alert_status) }
+
+  before do
+    project.add_developer(user)
+  end
+
+  it 'updates the status of the alert' do
+    post_graphql_mutation(mutation, current_user: user)
+
+    expect(response).to have_gitlab_http_status(:success)
+    expect(mutation_response['alert']['status']).to eq(input[:status])
+  end
+end