Add SlackSource spec

dev.yml

@@ -3,4 +3,3 @@ name: lita-slack
 up:
   - ruby:
       version: 2.4.3
-  - railgun

lib/lita/adapters/slack.rb

@@ -133,7 +133,7 @@ def room_roster(room_id, api)
 
       def try_get(object, attribute)
         if object.respond_to? attribute
-          object.attribute
+          object.send(attribute)
         else
           nil
         end

spec/lita/adapters/slack/slack_source_spec.rb

@@ -0,0 +1,36 @@
+require "spec_helper"
+
+describe Lita::Adapters::Slack::SlackSource, lita: true do
+  subject { described_class.new(room: room_source, extensions: extensions) }
+
+  let(:room_source) { Lita::Source.new(room: 'C024BE91L') }
+
+  describe "with timestamps" do
+    let(:extensions) do
+      { 
+        :timestamp => "123456.789",
+        :thread_ts => "98765.12" 
+      }
+    end
+
+    it "can read timestamp" do
+      expect(subject.timestamp).to eq("123456.789")
+    end
+
+    it "can read thread_ts" do
+      expect(subject.thread_ts).to eq("98765.12")
+    end
+  end
+
+  describe "without extensions" do
+    let(:extensions) { { } }
+
+    it "can read timestamp" do
+      expect(subject.timestamp).to eq(nil)
+    end
+
+    it "can read thread_ts" do
+      expect(subject.thread_ts).to eq(nil)
+    end
+  end
+end