diff --git a/Makefile b/Makefile
index 5901f77..5efdc36 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@ PROJECT = katana
 DEPS = eper aleppo xref_runner
 SHELL_DEPS := sync
 TEST_DEPS = mixer
-LOCAL_DEPS := xmerl tools compiler syntax_tools common_test inets ssl test_server dialyzer wx
+LOCAL_DEPS := xmerl tools compiler syntax_tools common_test inets ssl test_server hipe public_key dialyzer wx
 
 dep_eper = git https://github.com/massemanet/eper.git 0.96.3
 dep_sync = git https://github.com/inaka/sync.git 0.1.3
diff --git a/src/ktn_random.erl b/src/ktn_random.erl
index d315b78..6e07d64 100644
--- a/src/ktn_random.erl
+++ b/src/ktn_random.erl
@@ -37,11 +37,12 @@ generate() ->
 generate(Length) ->
     gen_server:call(?MODULE, {random_string, Length}).
 
--spec uniform(non_neg_integer()) -> non_neg_integer().
+-spec uniform(term()) -> non_neg_integer() | {error, {invalid_value, term()}}.
 uniform(Max) ->
     gen_server:call(?MODULE, {random_uniform, Max}).
 
--spec uniform(non_neg_integer(), non_neg_integer()) -> non_neg_integer().
+-spec uniform(term(), term()) ->
+    non_neg_integer() | {error, {invalid_range, term(), term()}}.
 uniform(Min, Max) ->
     gen_server:call(?MODULE, {random_uniform, Min, Max}).
 
diff --git a/src/ktn_recipe.erl b/src/ktn_recipe.erl
index 0972bde..cbe9d4c 100644
--- a/src/ktn_recipe.erl
+++ b/src/ktn_recipe.erl
@@ -37,7 +37,7 @@ run(Mod, InitialState) when is_atom(Mod) ->
 -spec run(transitions(), step_fun(), step_fun(), term()) -> term().
 run(Transitions, ResultFun, ErrorFun, InitialState) ->
   NormalizedTransitions = normalize(Transitions),
-  InitialFun            = initial_fun(Transitions),
+  InitialFun            = initial_fun(NormalizedTransitions),
   run(NormalizedTransitions, InitialFun, ResultFun, ErrorFun, InitialState).
 
 -spec run(normalized_transitions(), output(), step_fun(), step_fun(), term()) ->
@@ -66,11 +66,7 @@ run(Transitions, StepFun, ResultFun, ErrorFun, State) ->
   end.
 
 -spec initial_fun(normalized_transitions()) -> step_fun().
-initial_fun(Transitions) ->
-  case hd(Transitions) of
-    {InitialFun, _, _} -> InitialFun;
-    InitialFun         -> InitialFun
-  end.
+initial_fun([{InitialFun, _, _} | _]) -> InitialFun.
 
 -spec normalize(module() | transitions()) -> normalized_transitions().
 normalize(Mod) when is_atom(Mod) ->
diff --git a/src/ktn_recipe_verify.erl b/src/ktn_recipe_verify.erl
index cf90b3e..5825939 100644
--- a/src/ktn_recipe_verify.erl
+++ b/src/ktn_recipe_verify.erl
@@ -24,11 +24,11 @@
                   , error => error()
                   }.
 
--spec transitions() -> verify_exports
-                     | verify_normalizability
-                     | verify_transitions
-                     | verify_transition_exports
-                     .
+-spec transitions() -> [ verify_exports
+                       | verify_normalizability
+                       | verify_transitions
+                       | verify_transition_exports
+                       ].
 transitions() ->
   [ verify_exports
   , verify_normalizability
diff --git a/src/ktn_user_default.erl b/src/ktn_user_default.erl
index fa52810..170a1eb 100644
--- a/src/ktn_user_default.erl
+++ b/src/ktn_user_default.erl
@@ -14,7 +14,7 @@ xref() ->
 cmd(Cmd) ->
     io:format("~s~n", [os:cmd(Cmd)]).
 
--spec all_modules() -> module().
+-spec all_modules() -> [module()].
 all_modules() ->
   [ list_to_atom(
       re:replace(
diff --git a/test/ktn_binary_SUITE.erl b/test/ktn_binary_SUITE.erl
index 98219f9..22fbdc6 100644
--- a/test/ktn_binary_SUITE.erl
+++ b/test/ktn_binary_SUITE.erl
@@ -46,7 +46,7 @@ end_per_suite(Config) ->
 -spec join(config()) -> ok.
 join(_Config) ->
     Binaries = [<<"foo">>, <<"bar">>, <<"buzz">>],
-    
     <<>> = ktn_binary:join([], <<", ">>),
     <<"foo">> = ktn_binary:join([<<"foo">>], <<", ">>),
-    <<"foo, bar, buzz">> = ktn_binary:join(Binaries, <<", ">>).
+    <<"foo, bar, buzz">> = ktn_binary:join(Binaries, <<", ">>),
+    ok.
diff --git a/test/ktn_code_SUITE.erl b/test/ktn_code_SUITE.erl
index d9da80e..ff959ad 100644
--- a/test/ktn_code_SUITE.erl
+++ b/test/ktn_code_SUITE.erl
@@ -53,13 +53,14 @@ consult(_Config) ->
 
     [{'.'}] = ktn_code:consult("{'.'}.\n"),
     [{<<"ble.bla">>}, {"github.com"}] =
-        ktn_code:consult("{<<\"ble.bla\">>}.\n{\"github.com\"}.\r\n").
-
+        ktn_code:consult("{<<\"ble.bla\">>}.\n{\"github.com\"}.\r\n"),
+    ok.
 
 -spec beam_to_string(config()) -> ok.
 beam_to_string(_Config) ->
     {error, beam_lib, _} = ktn_code:beam_to_string(bla),
-    {ok, _} = ktn_code:beam_to_string("../../ebin/ktn_code.beam").
+    {ok, _} = ktn_code:beam_to_string("../../ebin/ktn_code.beam"),
+    ok.
 
 parse_tree(_Config) ->
     ModuleNode = #{type => module,
diff --git a/test/ktn_lists_SUITE.erl b/test/ktn_lists_SUITE.erl
index b206a4e..9adf24d 100644
--- a/test/ktn_lists_SUITE.erl
+++ b/test/ktn_lists_SUITE.erl
@@ -54,7 +54,8 @@ delete_first(_Config) ->
     [4] = ktn_lists:delete_first(Fun, [4, 4]),
     [1, 3] = ktn_lists:delete_first(Fun, [1, 3]),
     [1, 3] = ktn_lists:delete_first(Fun, [1, 4, 3]),
-    [1, 3, 4] = ktn_lists:delete_first(Fun, [1, 4, 3, 4]).
+    [1, 3, 4] = ktn_lists:delete_first(Fun, [1, 4, 3, 4]),
+    ok.
 
 -spec split_when(config()) -> ok.
 split_when(_Config) ->
@@ -65,7 +66,8 @@ split_when(_Config) ->
     ["."] = ktn_lists:split_when(IsDot, "."),
     ["{a}.", " {b}.", "{c, d, e}"] =
         ktn_lists:split_when(IsDot, "{a}. {b}.{c, d, e}"),
-    ["{a} {b}{c, d, e}"] = ktn_lists:split_when(IsDot, "{a} {b}{c, d, e}").
+    ["{a} {b}{c, d, e}"] = ktn_lists:split_when(IsDot, "{a} {b}{c, d, e}"),
+    ok.
 
 -spec map(config()) -> ok.
 map(_Config) ->
@@ -76,7 +78,8 @@ map(_Config) ->
     [2, 4, 6] = ktn_lists:map(Multiply, [2], [1, 2, 3]),
 
     SumMultiply = fun(X, Y, Z) -> (X + Y) * Z end,
-    [30, 40, 50] = ktn_lists:map(SumMultiply, [2, 10], [1, 2, 3]).
+    [30, 40, 50] = ktn_lists:map(SumMultiply, [2, 10], [1, 2, 3]),
+    ok.
 
 -spec filter(config()) -> ok.
 filter(_Config) ->
@@ -87,4 +90,5 @@ filter(_Config) ->
     [3] = ktn_lists:filter(Multiply, [2], [1, 2, 3]),
 
     SumMultiply = fun(X, Y, Z) -> (X + Y) * Z =/= 30 end,
-    [2, 3] = ktn_lists:filter(SumMultiply, [2, 10], [1, 2, 3]).
+    [2, 3] = ktn_lists:filter(SumMultiply, [2, 10], [1, 2, 3]),
+    ok.
diff --git a/test/ktn_maps_SUITE.erl b/test/ktn_maps_SUITE.erl
index 6616fd6..8c89b2a 100644
--- a/test/ktn_maps_SUITE.erl
+++ b/test/ktn_maps_SUITE.erl
@@ -58,7 +58,8 @@ end_per_suite(Config) ->
 find_nested_values(Config) ->
     Map = proplists:get_value(map, Config),
     8080 = ktn_maps:get([conversation, destination, port], Map),
-    1.5 = ktn_maps:get([location, latitude], Map).
+    1.5 = ktn_maps:get([location, latitude], Map),
+    ok.
 
 -spec find_shallow_values(config()) -> ok.
 find_shallow_values(Config) ->
@@ -66,7 +67,8 @@ find_shallow_values(Config) ->
     "john.doe" = ktn_maps:get(user, Map),
     "John" = ktn_maps:get(name, Map),
     "Doe" = ktn_maps:get(last_name, Map),
-    "john.doe" = ktn_maps:get([user], Map).
+    "john.doe" = ktn_maps:get([user], Map),
+    ok.
 
 -spec dont_find_nested_values(config()) -> ok.
 dont_find_nested_values(Config) ->
@@ -80,7 +82,8 @@ dont_find_nested_values(Config) ->
              ktn_maps:get([social, facebook], Map)
          catch
              error:bad_path -> ok
-         end.
+         end,
+    ok.
 
 -spec dont_find_shallow_values(config()) -> ok.
 dont_find_shallow_values(Config) ->
@@ -99,7 +102,8 @@ dont_find_shallow_values(Config) ->
              ktn_maps:get([email], Map)
          catch
              error:bad_path -> ok
-         end.
+         end,
+    ok.
 
 -spec provide_default(config()) -> ok.
 provide_default(Config) ->
@@ -118,4 +122,5 @@ provide_default(Config) ->
 
     default = ktn_maps:get(username, Map, default),
     default = ktn_maps:get(email, Map, default),
-    default = ktn_maps:get([email], Map, default).
+    default = ktn_maps:get([email], Map, default),
+    ok.
diff --git a/test/ktn_os_SUITE.erl b/test/ktn_os_SUITE.erl
index ade3147..7850686 100644
--- a/test/ktn_os_SUITE.erl
+++ b/test/ktn_os_SUITE.erl
@@ -48,7 +48,6 @@ command(_Config) ->
   ok = try ktn_os:command("sleep 5", #{timeout => 1000})
        catch _:timeout -> ok end,
 
-  Fun = fun() -> ktn_os:command("cd /; pwd") end,
   FilterFun =
     fun(Line) ->
         case re:run(Line, "=INFO REPORT==== .* ===") of
@@ -56,7 +55,13 @@ command(_Config) ->
           {match, _}-> true
         end
     end,
-  check_some_line_output(Fun, FilterFun),
+
+  ct:capture_start(),
+  {0, "/"} = ktn_os:command("cd /; pwd"),
+  ct:capture_stop(),
+  Lines = ct:capture_get([]),
+  ListFun = fun(Line) -> FilterFun(Line) end,
+  [_ | _] = lists:filter(ListFun, Lines),
 
   ct:comment("Check result when process is killed"),
   Self = self(),
@@ -67,17 +72,5 @@ command(_Config) ->
                end
            end,
   erlang:spawn_link(YesFun),
-  os:cmd("pkill yes"),
+  [] = os:cmd("pkill yes"),
   ok  = receive X -> X after 1000 -> error end.
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-%% Helper functions
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-
-check_some_line_output(Fun, FilterFun) ->
-  ct:capture_start(),
-  Fun(),
-  ct:capture_stop(),
-  Lines = ct:capture_get([]),
-  ListFun = fun(Line) -> FilterFun(Line) end,
-  [_ | _] = lists:filter(ListFun, Lines).
diff --git a/test/ktn_random_SUITE.erl b/test/ktn_random_SUITE.erl
index d406170..16ec3a0 100644
--- a/test/ktn_random_SUITE.erl
+++ b/test/ktn_random_SUITE.erl
@@ -55,7 +55,8 @@ init_per_testcase(_, Config) ->
 generate(_Config) ->
     true = is_list(ktn_random:generate()),
     16 = length(ktn_random:generate()),
-    25 = length(ktn_random:generate(25)).
+    25 = length(ktn_random:generate(25)),
+    ok.
 
 -spec uniform(config()) -> ok.
 uniform(_Config) ->
@@ -65,7 +66,8 @@ uniform(_Config) ->
 
     do_times(fun (_) -> in_range(ktn_random:uniform(5, 90), 5, 90) end, Times),
     {error, _} = ktn_random:uniform(165, 165),
-    {error, _} = ktn_random:uniform(15, 5).
+    {error, _} = ktn_random:uniform(15, 5),
+    ok.
 
 -spec pick(config()) -> ok.
 pick(_Config) ->
@@ -75,12 +77,7 @@ pick(_Config) ->
             List = lists:seq($a, $a + I),
             K = ktn_random:pick(List),
             true = lists:member(K, List)
-        end, lists:seq(1, 1000)),
-    try ktn_random:pick([]) of
-        K -> ct:fail("Unexpected result: ~p", [K])
-    catch
-        _:function_clause -> ok
-    end.
+        end, lists:seq(1, 1000)).
 
 do_times(Fun, N) ->
     lists:foreach(Fun, lists:seq(1, N)).
diff --git a/test/secure_vault.erl b/test/secure_vault.erl
index 2e8a906..cad4278 100644
--- a/test/secure_vault.erl
+++ b/test/secure_vault.erl
@@ -29,6 +29,8 @@
         , closed/2
         ]).
 
+-dialyzer({no_missing_calls, [start/2]}).
+
 start(MasterPassword, MaxAttempts) ->
   ktn_fsm:start(
     ?MODULE,