until now observeSubject works exactly like observe. First <really interesting> failing test

beholder.lua

@@ -121,6 +121,13 @@ function beholder.observe(...)
   return addCallbackToNode(node, callback)
 end
 
+function beholder.observeSubject(subject, ...)
+  assert(subject ~= nil, "Subject was nil. Please provide a valid subject")
+  local event, callback = extractEventAndCallbackFromParams({...})
+  local node = findOrCreateDescendantNode(root, event)
+  return addCallbackToNode(node, callback)
+end
+
 function beholder.stopObserving(id)
   local node = findNodeById(id)
   if not node then return false end

spec/acceptance.lua

@@ -26,6 +26,26 @@ describe("Acceptance", function()
 
   end)
 
+  test("Observing subjects", function()
+    local counter = 0
+    local button = {}
+
+    beholder.observeSubject(button, "EVENT", function() counter = counter + 1 end)
+
+    beholder.trigger("EVENT")
+    beholder.trigger("EVENT")
+
+    assert_equal(2, counter)
+
+    button = nil
+    collectgarbage("collect")
+
+    beholder.trigger("EVENT")
+
+    assert_equal(2, counter)
+
+  end)
+
   test("several actions on the same event", function()
 
     local counter1, counter2 = 0,0

spec/unit.lua

@@ -54,6 +54,72 @@ describe("Unit", function()
     end)
   end)
 
+  describe(".observeSubject", function()
+    it("throws an error if subject is nil", function()
+      assert_error(function() beholder.observeSubject(nil, 'blah') end)
+    end)
+
+    it("notices simple events so that trigger works", function()
+      local counter = 0
+      local button = {}
+      beholder.observeSubject(button, "PUSH", function() counter = counter + 1 end)
+      beholder.trigger("PUSH")
+      assert_equal(counter, 1)
+    end)
+
+    it("remembers if more than one action is associated to the same event", function()
+      local counter1, counter2 = 0,0
+      local button = {}
+      beholder.observeSubject(button, "PUSH", function() counter1 = counter1 + 1 end)
+      beholder.observeSubject(button, "PUSH", function() counter2 = counter2 + 1 end)
+      beholder.trigger("PUSH")
+      assert_equal(counter1, 1)
+      assert_equal(counter2, 1)
+    end)
+
+    it("allows observing composed events", function()
+      local counter = 0
+      local button = {}
+      beholder.observeSubject(button, "PUSH", "start", function() counter = counter + 1 end)
+      beholder.trigger("PUSH", "start")
+      assert_equal(counter, 1)
+    end)
+
+    it("observes all events with the nil event", function()
+      local counter = 0
+      local button = {}
+      beholder.observeSubject(button, function(_,x) counter = counter + x end)
+      beholder.trigger("FOO", 1)
+      beholder.trigger("BAR", 2)
+      assert_equal(3, counter)
+    end)
+
+    it("does not store hard references to variables", function()
+      local counter = 0
+      local x = {}
+      local button = {}
+      beholder.observeSubject(button, x, function() counter = counter + 1 end)
+      beholder.triggerAll()
+      x = nil
+      collectgarbage("collect")
+      beholder.triggerAll()
+      assert_equal(1, counter)
+    end)
+
+    it("does not react to triggers once the subject has been garbage-collected", function()
+      local counter = 0
+      local button = {}
+      beholder.observeSubject(button, "PUSH", function() counter = counter + 1 end)
+      beholder.trigger("PUSH")
+      assert_equal(1, counter)
+      button = nil
+      collectgarbage("collect")
+      beholder.trigger("PUSH")
+      assert_equal(1, counter)
+
+    end)
+  end)
+
   describe(".stopObserving", function()
     it("stops noticing events so trigger doesn't work any more", function()
       local counter = 0