diff --git a/src/resources.jl b/src/resources.jl
index 67777e6..966d24e 100644
--- a/src/resources.jl
+++ b/src/resources.jl
@@ -3,8 +3,11 @@ play_sound(filename::String, loops::Integer)
 
 Plays a sound effect from the `sounds` subdirctory. It will play the specified number of times. If not specified, it will default to once.
 """
-play_sound = let cache=Dict{Symbol,Ptr}()
-    function _play_sound(name, loops=0, ticks=-1)
+function play_sound end
+let cache=Dict{Symbol,Ptr}()
+    global  play_sound
+    function play_sound(name, loops=0, ticks=-1)
+        sound_file=""
         sample=get(cache,Symbol(name)) do
             sound_file = file_path(String(name), :sounds)
             Mix_LoadWAV(sound_file)
@@ -13,7 +16,7 @@ play_sound = let cache=Dict{Symbol,Ptr}()
             @warn "Could not load sound file: $sound_file\n$(getSDLError())"
             return
         else
-            cache[Symbol(name)]=sample
+            get!(cache,Symbol(name),sample)
         end
         r = Mix_PlayChannelTimed(Int32(-1), sample, loops, ticks)
         if r == -1
@@ -28,10 +31,22 @@ play_music(name::String, loops::Integer)
 
 Plays music from the `sounds` subdirectory. It will play the file the specified number of times. If not specified, it will default to infinitely.
 """
-function play_music(name, loops=-1)
-    music_file = file_path(name, :music)
-    music = Mix_LoadMUS(music_file)
-    Mix_PlayMusic( music, Int32(loops) )
+function play_music end
+let cache=Dict{Symbol,Ptr}()
+    global play_music
+    function play_music(name, loops=-1)
+        music_file = ""
+        music = get(cache,Symbol(name)) do
+            music_file = file_path(name, :music)
+            Mix_LoadMUS(music_file)
+        end
+        if music == C_NULL
+            error( "Could not load music file: $music_file\n$(getSDLError())" )
+        else
+            get!(cache,Symbol(name),music)
+        end
+        Mix_PlayMusic( music, Int32(loops) )
+    end
 end
 
 const resource_ext = Dict(
@@ -46,7 +61,7 @@ image_surface = let cache=Dict{Symbol,Ptr}()
             image_file = file_path(String(image), :images)
             sf = IMG_Load(image_file)
             if sf == C_NULL
-                throw("Error loading $image_file")
+                error("Error loading $image_file")
             end
             sf
         end
diff --git a/src/timer.jl b/src/timer.jl
index 1777022..fec742d 100644
--- a/src/timer.jl
+++ b/src/timer.jl
@@ -135,7 +135,7 @@ function tick(x::ContingentScheduled, elapsed, s=scheduler[])
         if r == nothing
             return
         else
-            push!(s, ContingetScheduled(x.action, 1e9*r+elapsed))
+            push!(s, ContingentScheduled(x.action, 1e9*r+elapsed))
         end
     end
 end
diff --git a/test/runtests.jl b/test/runtests.jl
index 37afb84..8da95a4 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -117,4 +117,92 @@ let ev=GameZero.SDL_Event(ntuple(UInt8,56))
     @test ev.window.event==0x0d
 end
 
-include("examples.jl")
\ No newline at end of file
+@testset "timer" begin
+    GameZero.scheduler[] = GameZero.Scheduler()
+    flag=false
+    f()= (flag=true;nothing)
+
+    @testset "once" begin
+        flag=false
+        schedule_once(f,1)
+        schedule_once(f,0.5)
+        @test flag==false
+        sleep(0.5)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+        flag=false
+        sleep(0.5)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+    end
+
+    @testset "unique" begin
+        flag=false
+        schedule_once(f,1)
+        schedule_unique(f,0.5)
+        @test flag==false
+        sleep(0.5)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+        flag=false
+        sleep(0.5)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==false
+    end
+    
+    @testset "interval" begin
+        flag=false
+        schedule_interval(f,1)
+        @test flag==false
+        sleep(1)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+        flag=false
+        sleep(1)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+        GameZero.clear!(GameZero.scheduler[])
+    end
+
+    function schedule_conti(f::Function, interval)
+        push!(GameZero.scheduler[], GameZero.ContingentScheduled(WeakRef(f), GameZero.elapsed(scheduler[])+interval*1e9))
+    end
+    f2()=(flag=true;0.5)
+    @testset "contingent" begin
+        flag=false
+        schedule_conti(f,1)
+        @test flag==false
+        sleep(1)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+
+        flag=false
+        schedule_conti(f2,1)
+        @test flag==false
+        sleep(1)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+        flag=false
+        sleep(0.5)
+        GameZero.tick!(GameZero.scheduler[])
+        @test flag==true
+    end
+
+end
+
+
+include("examples.jl")
+
+@testset "File not exist" begin
+    GameZero.file_path(name::String,subdir::Symbol)=throw(ArgumentError("File not exist"))
+    @test_throws ArgumentError play_music("filenotexist")
+    @test_throws ArgumentError play_sound("filenotexist")
+    @test_throws ArgumentError GameZero.image_surface("filenotexist")
+end
+
+@testset "Invalid file" begin
+    GameZero.file_path(name::String,subdir::Symbol)=@__FILE__
+    @test_throws ErrorException play_music("invalidfile")
+    @test_logs (:warn,r"Could not load") play_sound("invalidfile")
+    @test_throws ErrorException GameZero.image_surface("invalidfile")
+end
\ No newline at end of file