Fix mattermost icon selection

lib/discourse_chat/provider/mattermost/mattermost_provider.rb

@@ -44,7 +44,7 @@ module DiscourseChat
         end
 
         icon_url =
-          if !SiteSetting.chat_integration_slack_icon_url.blank?
+          if !SiteSetting.chat_integration_mattermost_icon_url.blank?
             UrlHelper.absolute(SiteSetting.chat_integration_mattermost_icon_url)
           elsif !SiteSetting.logo_small_url.blank?
             UrlHelper.absolute(SiteSetting.logo_small_url)

spec/lib/discourse_chat/provider/mattermost/mattermost_provider_spec.rb

@@ -7,6 +7,7 @@ RSpec.describe DiscourseChat::Provider::MattermostProvider do
     before do
       SiteSetting.chat_integration_mattermost_enabled = true
       SiteSetting.chat_integration_mattermost_webhook_url = "https://mattermost.blah/hook/abcd"
+      SiteSetting.logo_small_url = "https://some_small_logo"
     end
 
     let(:chan1) { DiscourseChat::Channel.create!(provider: 'mattermost', data: { identifier: "#awesomechannel" }) }
@@ -17,6 +18,21 @@ RSpec.describe DiscourseChat::Provider::MattermostProvider do
       expect(stub1).to have_been_requested.once
     end
 
+    describe 'when mattermost icon is not configured' do
+      it 'defaults to the right icon' do
+        message = described_class.mattermost_message(post, chan1)
+        expect(message[:icon_url]).to eq(SiteSetting.logo_small_url)
+      end
+    end
+
+    describe 'when mattermost icon has been configured' do
+      it 'should use the right icon' do
+        SiteSetting.chat_integration_mattermost_icon_url = "https://specific_logo"
+        message = described_class.mattermost_message(post, chan1)
+        expect(message[:icon_url]).to eq(SiteSetting.chat_integration_mattermost_icon_url)
+      end
+    end
+
     it 'handles errors correctly' do
       stub1 = stub_request(:post, "https://mattermost.blah/hook/abcd").to_return(status: 500, body: "error")
       expect(stub1).to have_been_requested.times(0)