Merge branch 'peppe/common_test_r14_dev_2' into dev

* peppe/common_test_r14_dev_2:
  Misc documentation updates
  Add documentation for run_test program
  Step vsn for test_server to 3.4
  Make {repeat*,N} property in group execute the group N times exactly
  Fix so that ct_run converts relative diretories in the code path to absolute
  Fix bug in handling framework:end_tc timeouts
  Fix bug that prevents the interactive shell mode to start properly
  Fix failing multiply timetrap test case
  Minor fixes in code and test suites
  Add support for executing pre-loaded suites (e.g. modules loaded as binaries)
  Add test suite for remote loading of binary suites
  Fix error with {repeat,0} property in groups causing double iterations
  Add support for config info functions (e.g. init_per_suite/0)
  Add support for dynamic timetrap handling
  Have end_per_testcase run even after timetrap_timeout and abort_testcase
  Flush old DOWN messages in demonitor
  Add groups in test specifications
  Add new tests for test case groups and test specifications
  Improve and fix various test suites
  Add event_handler_init start flag that can pass init arguments to event handlers
  ...

OTP-8703 peppe/common_test_r14_dev_2

1 files changed, 280 insertions, 35 deletions

diff --git a/lib/common_test/src/ct_testspec.erl b/lib/common_test/src/ct_testspec.erl
index 4378ec5a52..0f68b062f6 100644
--- a/lib/common_test/src/ct_testspec.erl
+++ b/lib/common_test/src/ct_testspec.erl
@@ -17,7 +17,7 @@
 %% %CopyrightEnd%
 %%
 
-%%% @doc Common Test Framework functions handlig test specifikations.
+%%% @doc Common Test Framework functions handling test specifications.
 %%%
 %%% <p>This module exports functions that are used within CT to
 %%% scan and parse test specifikations.</p>
@@ -270,33 +270,8 @@ collect_tests(Terms,TestSpec,Relaxed) ->
     put(relaxed,Relaxed),
     TestSpec1 = get_global(Terms,TestSpec),
     TestSpec2 = get_all_nodes(Terms,TestSpec1),
-    case catch evaluate(Terms,TestSpec2) of
-	{error,{Node,{M,F,A},Reason}} ->
-	    io:format("Error! Common Test failed to evaluate ~w:~w/~w on ~w. "
-		      "Reason: ~p~n~n", [M,F,A,Node,Reason]);
-	_ -> ok
-    end,
-    add_tests(Terms,TestSpec2).
-    
-evaluate([{eval,NodeRef,{M,F,Args}}|Ts],Spec) ->
-    Node = ref2node(NodeRef,Spec#testspec.nodes),
-    case rpc:call(Node,M,F,Args) of
-	{badrpc,Reason} ->
-	    throw({error,{Node,{M,F,length(Args)},Reason}});
-	_ ->
-	    ok
-    end,
-    evaluate(Ts,Spec);
-evaluate([{eval,{M,F,Args}}|Ts],Spec) ->
-    case catch apply(M,F,Args) of
-	{'EXIT',Reason} ->
-	    throw({error,{node(),{M,F,length(Args)},Reason}});
-	_ ->
-	    ok
-    end,
-    evaluate(Ts,Spec);
-evaluate([],_Spec) ->
-    ok.
+    {Terms2, TestSpec3} = filter_init_terms(Terms, [], TestSpec2),
+    add_tests(Terms2,TestSpec3).
 
 get_global([{alias,Ref,Dir}|Ts],Spec=#testspec{alias=Refs}) ->
     get_global(Ts,Spec#testspec{alias=[{Ref,get_absdir(Dir,Spec)}|Refs]});
@@ -305,6 +280,26 @@ get_global([{node,Ref,Node}|Ts],Spec=#testspec{nodes=Refs}) ->
 get_global([_|Ts],Spec) -> get_global(Ts,Spec);
 get_global([],Spec) -> Spec.
 
+get_absfile(Callback, FullName,#testspec{spec_dir=SpecDir}) ->
+    % we need to temporary switch to new cwd here, because
+    % otherwise config files cannot be found
+    {ok, OldWd} = file:get_cwd(),
+    ok = file:set_cwd(SpecDir),
+    R =  Callback:check_parameter(FullName),
+    ok = file:set_cwd(OldWd),
+    case R of
+	{ok, {file, FullName}}->
+	    File = filename:basename(FullName),
+	    Dir = get_absname(filename:dirname(FullName),SpecDir),
+	    filename:join(Dir,File);
+	{ok, {config, FullName}}->
+	    FullName;
+	{error, {nofile, FullName}}->
+	    FullName;
+	{error, {wrong_config, FullName}}->
+	    FullName
+    end.
+
 get_absfile(FullName,#testspec{spec_dir=SpecDir}) ->
     File = filename:basename(FullName),
     Dir = get_absname(filename:dirname(FullName),SpecDir),
@@ -353,6 +348,68 @@ get_all_nodes([_|Ts],Spec) ->
 get_all_nodes([],Spec) ->
     Spec.
 
+filter_init_terms([{init, InitOptions}|Ts], NewTerms, Spec)->
+    filter_init_terms([{init, list_nodes(Spec), InitOptions}|Ts], NewTerms, Spec);
+filter_init_terms([{init, NodeRef, InitOptions}|Ts], NewTerms, Spec)
+    when is_atom(NodeRef)->
+    filter_init_terms([{init, [NodeRef], InitOptions}|Ts], NewTerms, Spec);
+filter_init_terms([{init, NodeRefs, InitOption}|Ts], NewTerms, Spec) when is_tuple(InitOption) ->
+    filter_init_terms([{init, NodeRefs, [InitOption]}|Ts], NewTerms, Spec);
+filter_init_terms([{init, [NodeRef|NodeRefs], InitOptions}|Ts], NewTerms, Spec=#testspec{init=InitData})->
+    NodeStartOptions = case lists:keyfind(node_start, 1, InitOptions) of
+	{node_start, NSOptions}->
+	    case lists:keyfind(callback_module, 1, NSOptions) of
+		{callback_module, _Callback}->
+		    NSOptions;
+		false->
+		    [{callback_module, ct_slave}|NSOptions]
+	    end;
+	false->
+	    []
+    end,
+    EvalTerms = case lists:keyfind(eval, 1, InitOptions) of
+	{eval, MFA} when is_tuple(MFA)->
+	    [MFA];
+	{eval, MFAs} when is_list(MFAs)->
+	    MFAs;
+	false->
+	    []
+    end,
+    Node = ref2node(NodeRef,Spec#testspec.nodes),
+    InitData2 = add_option({node_start, NodeStartOptions}, Node, InitData, true),
+    InitData3 = add_option({eval, EvalTerms}, Node, InitData2, false),
+    filter_init_terms([{init, NodeRefs, InitOptions}|Ts], NewTerms, Spec#testspec{init=InitData3});
+filter_init_terms([{init, [], _}|Ts], NewTerms, Spec)->
+    filter_init_terms(Ts, NewTerms, Spec);
+filter_init_terms([Term|Ts], NewTerms, Spec)->
+    filter_init_terms(Ts, [Term|NewTerms], Spec);
+filter_init_terms([], NewTerms, Spec)->
+    {lists:reverse(NewTerms), Spec}.
+
+add_option([], _, List, _)->
+    List;
+add_option({Key, Value}, Node, List, WarnIfExists) when is_list(Value)->
+    OldOptions = case lists:keyfind(Node, 1, List) of
+	{Node, Options}->
+	    Options;
+	false->
+	    []
+    end,
+    NewOption = case lists:keyfind(Key, 1, OldOptions) of
+	{Key, OldOption} when WarnIfExists, OldOption/=[]->
+	    io:format("There is an option ~w=~w already defined for node ~p, skipping new ~w~n",
+		[Key, OldOption, Node, Value]),
+	    OldOption;
+	{Key, OldOption}->
+	    OldOption ++ Value;
+	false->
+	    Value
+    end,
+    lists:keystore(Node, 1, List,
+	{Node, lists:keystore(Key, 1, OldOptions, {Key, NewOption})});
+add_option({Key, Value}, Node, List, WarnIfExists)->
+    add_option({Key, [Value]}, Node, List, WarnIfExists).
+
 save_nodes(Nodes,Spec=#testspec{nodes=NodeRefs}) ->
     NodeRefs1 =
 	lists:foldr(fun(all_nodes,NR) ->
@@ -415,6 +472,36 @@ add_tests([{cover,Node,File}|Ts],Spec) ->
 add_tests([{cover,File}|Ts],Spec) ->
     add_tests([{cover,all_nodes,File}|Ts],Spec);
 
+%% --- multiply_timetraps ---
+add_tests([{multiply_timetraps,all_nodes,MT}|Ts],Spec) ->
+    Tests = lists:map(fun(N) -> {multiply_timetraps,N,MT} end, list_nodes(Spec)),
+    add_tests(Tests++Ts,Spec);
+add_tests([{multiply_timetraps,Nodes,MT}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,multiply_timetraps,[MT],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{multiply_timetraps,Node,MT}|Ts],Spec) ->
+    MTs = Spec#testspec.multiply_timetraps,
+    MTs1 = [{ref2node(Node,Spec#testspec.nodes),MT} |
+	    lists:keydelete(ref2node(Node,Spec#testspec.nodes),1,MTs)],
+    add_tests(Ts,Spec#testspec{multiply_timetraps=MTs1});
+add_tests([{multiply_timetraps,MT}|Ts],Spec) ->
+    add_tests([{multiply_timetraps,all_nodes,MT}|Ts],Spec);
+
+%% --- scale_timetraps ---
+add_tests([{scale_timetraps,all_nodes,ST}|Ts],Spec) ->
+    Tests = lists:map(fun(N) -> {scale_timetraps,N,ST} end, list_nodes(Spec)),
+    add_tests(Tests++Ts,Spec);
+add_tests([{scale_timetraps,Nodes,ST}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,scale_timetraps,[ST],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{scale_timetraps,Node,ST}|Ts],Spec) ->
+    STs = Spec#testspec.scale_timetraps,
+    STs1 = [{ref2node(Node,Spec#testspec.nodes),ST} |
+	    lists:keydelete(ref2node(Node,Spec#testspec.nodes),1,STs)],
+    add_tests(Ts,Spec#testspec{scale_timetraps=STs1});
+add_tests([{scale_timetraps,ST}|Ts],Spec) ->
+    add_tests([{scale_timetraps,all_nodes,ST}|Ts],Spec);
+
 %% --- config ---
 add_tests([{config,all_nodes,Files}|Ts],Spec) ->
     Tests = lists:map(fun(N) -> {config,N,Files} end, list_nodes(Spec)),
@@ -434,6 +521,27 @@ add_tests([{config,Node,F}|Ts],Spec) ->
 add_tests([{config,Files}|Ts],Spec) ->
     add_tests([{config,all_nodes,Files}|Ts],Spec);
 
+
+%% --- userconfig ---
+add_tests([{userconfig,all_nodes,CBF}|Ts],Spec) ->
+    Tests = lists:map(fun(N) -> {userconfig,N,CBF} end, list_nodes(Spec)),
+    add_tests(Tests++Ts,Spec);
+add_tests([{userconfig,Nodes,CBF}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,userconfig,[CBF],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{userconfig,Node,[{Callback, Config}|CBF]}|Ts],Spec) ->
+    Cfgs = Spec#testspec.userconfig,
+    Node1 = ref2node(Node,Spec#testspec.nodes),
+    add_tests([{userconfig,Node,CBF}|Ts],
+	      Spec#testspec{userconfig=[{Node1,{Callback,
+				get_absfile(Callback, Config ,Spec)}}|Cfgs]});
+add_tests([{userconfig,_Node,[]}|Ts],Spec) ->
+    add_tests(Ts,Spec);
+add_tests([{userconfig,Node,CBF}|Ts],Spec) ->
+    add_tests([{userconfig,Node,[CBF]}|Ts],Spec);
+add_tests([{userconfig,CBF}|Ts],Spec) ->
+    add_tests([{userconfig,all_nodes,CBF}|Ts],Spec);
+
 %% --- event_handler ---
 add_tests([{event_handler,all_nodes,Hs}|Ts],Spec) ->
     Tests = lists:map(fun(N) -> {event_handler,N,Hs,[]} end, list_nodes(Spec)),
@@ -516,6 +624,38 @@ add_tests([{suites,Node,Dir,Ss}|Ts],Spec) ->
 			   Ss,Tests),
     add_tests(Ts,Spec#testspec{tests=Tests1});
 
+%% --- groups ---
+%% Later make it possible to specify group execution properties
+%% that will override thse in the suite. Also make it possible
+%% create dynamic groups in specification, i.e. to group test cases
+%% by means of groups defined only in the test specification.
+add_tests([{groups,all_nodes,Dir,Suite,Gs}|Ts],Spec) ->
+    add_tests([{groups,list_nodes(Spec),Dir,Suite,Gs}|Ts],Spec);
+add_tests([{groups,all_nodes,Dir,Suite,Gs,{cases,TCs}}|Ts],Spec) ->
+    add_tests([{groups,list_nodes(Spec),Dir,Suite,Gs,{cases,TCs}}|Ts],Spec);
+add_tests([{groups,Dir,Suite,Gs}|Ts],Spec) ->
+    add_tests([{groups,all_nodes,Dir,Suite,Gs}|Ts],Spec);
+add_tests([{groups,Dir,Suite,Gs,{cases,TCs}}|Ts],Spec) ->
+    add_tests([{groups,all_nodes,Dir,Suite,Gs,{cases,TCs}}|Ts],Spec);
+add_tests([{groups,Nodes,Dir,Suite,Gs}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,groups,[Dir,Suite,Gs],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{groups,Nodes,Dir,Suite,Gs,{cases,TCs}}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,groups,[Dir,Suite,Gs,{cases,TCs}],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{groups,Node,Dir,Suite,Gs}|Ts],Spec) ->
+    Tests = Spec#testspec.tests,
+    Tests1 = insert_groups(ref2node(Node,Spec#testspec.nodes),
+			   ref2dir(Dir,Spec#testspec.alias),
+			   Suite,Gs,all,Tests),
+    add_tests(Ts,Spec#testspec{tests=Tests1});
+add_tests([{groups,Node,Dir,Suite,Gs,{cases,TCs}}|Ts],Spec) ->
+    Tests = Spec#testspec.tests,
+    Tests1 = insert_groups(ref2node(Node,Spec#testspec.nodes),
+			   ref2dir(Dir,Spec#testspec.alias),
+			   Suite,Gs,TCs,Tests),
+    add_tests(Ts,Spec#testspec{tests=Tests1});
+
 %% --- cases ---
 add_tests([{cases,all_nodes,Dir,Suite,Cs}|Ts],Spec) ->
     add_tests([{cases,list_nodes(Spec),Dir,Suite,Cs}|Ts],Spec);
@@ -546,6 +686,34 @@ add_tests([{skip_suites,Node,Dir,Ss,Cmt}|Ts],Spec) ->
 			 Ss,Cmt,Tests),
     add_tests(Ts,Spec#testspec{tests=Tests1});
 
+%% --- skip_groups ---
+add_tests([{skip_groups,all_nodes,Dir,Suite,Gs,Cmt}|Ts],Spec) ->
+    add_tests([{skip_groups,list_nodes(Spec),Dir,Suite,Gs,Cmt}|Ts],Spec);
+add_tests([{skip_groups,all_nodes,Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec) ->
+    add_tests([{skip_groups,list_nodes(Spec),Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec);
+add_tests([{skip_groups,Dir,Suite,Gs,Cmt}|Ts],Spec) ->
+    add_tests([{skip_groups,all_nodes,Dir,Suite,Gs,Cmt}|Ts],Spec);
+add_tests([{skip_groups,Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec) ->
+    add_tests([{skip_groups,all_nodes,Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec);
+add_tests([{skip_groups,Nodes,Dir,Suite,Gs,Cmt}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,skip_groups,[Dir,Suite,Gs,Cmt],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{skip_groups,Nodes,Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec) when is_list(Nodes) ->
+    Ts1 = separate(Nodes,skip_groups,[Dir,Suite,Gs,{cases,TCs},Cmt],Ts,Spec#testspec.nodes),
+    add_tests(Ts1,Spec);
+add_tests([{skip_groups,Node,Dir,Suite,Gs,Cmt}|Ts],Spec) ->
+    Tests = Spec#testspec.tests,
+    Tests1 = skip_groups(ref2node(Node,Spec#testspec.nodes),
+			 ref2dir(Dir,Spec#testspec.alias),
+			 Suite,Gs,all,Cmt,Tests),
+    add_tests(Ts,Spec#testspec{tests=Tests1});
+add_tests([{skip_groups,Node,Dir,Suite,Gs,{cases,TCs},Cmt}|Ts],Spec) ->
+    Tests = Spec#testspec.tests,
+    Tests1 = skip_groups(ref2node(Node,Spec#testspec.nodes),
+			 ref2dir(Dir,Spec#testspec.alias),
+			 Suite,Gs,TCs,Cmt,Tests),
+    add_tests(Ts,Spec#testspec{tests=Tests1});
+
 %% --- skip_cases ---
 add_tests([{skip_cases,all_nodes,Dir,Suite,Cs,Cmt}|Ts],Spec) ->
     add_tests([{skip_cases,list_nodes(Spec),Dir,Suite,Cs,Cmt}|Ts],Spec);
@@ -614,8 +782,11 @@ separate([],_,_,_) ->
     
 
 %% Representation:
-%% {{Node,Dir},[{Suite1,[case11,case12,...]},{Suite2,[case21,case22,...]},...]}
-%% {{Node,Dir},[{Suite1,{skip,Cmt}},{Suite2,[{case21,{skip,Cmt}},case22,...]},...]}
+%% {{Node,Dir},[{Suite1,[GrOrCase11,GrOrCase12,...]},
+%%              {Suite2,[GrOrCase21,GrOrCase22,...]},...]}
+%% {{Node,Dir},[{Suite1,{skip,Cmt}},
+%%              {Suite2,[{GrOrCase21,{skip,Cmt}},GrOrCase22,...]},...]}
+%% GrOrCase = {GroupName,[Case1,Case2,...]} | Case
 
 insert_suites(Node,Dir,[S|Ss],Tests) ->
     Tests1 = insert_cases(Node,Dir,S,all,Tests),
@@ -625,6 +796,54 @@ insert_suites(_Node,_Dir,[],Tests) ->
 insert_suites(Node,Dir,S,Tests) ->
     insert_suites(Node,Dir,[S],Tests).
 
+insert_groups(Node,Dir,Suite,Group,Cases,Tests) when is_atom(Group) ->
+    insert_groups(Node,Dir,Suite,[Group],Cases,Tests);
+insert_groups(Node,Dir,Suite,Groups,Cases,Tests) when
+      ((Cases == all) or is_list(Cases)) and is_list(Groups) ->
+    case lists:keysearch({Node,Dir},1,Tests) of
+	{value,{{Node,Dir},[{all,_}]}} ->
+	    Tests;
+	{value,{{Node,Dir},Suites0}} ->
+	    Suites1 = insert_groups1(Suite,
+				     [{Gr,Cases} || Gr <- Groups],
+				     Suites0),
+	    insert_in_order({{Node,Dir},Suites1},Tests);
+	false ->
+	    Groups1 = [{Gr,Cases} || Gr <- Groups],
+	    insert_in_order({{Node,Dir},[{Suite,Groups1}]},Tests)
+    end;
+insert_groups(Node,Dir,Suite,Groups,Case,Tests) when is_atom(Case) ->
+    Cases = if Case == all -> all; true -> [Case] end,
+    insert_groups(Node,Dir,Suite,Groups,Cases,Tests).
+
+insert_groups1(_Suite,_Groups,all) ->
+    all;
+insert_groups1(Suite,Groups,Suites0) ->
+    case lists:keysearch(Suite,1,Suites0) of
+	{value,{Suite,all}} ->
+	    Suites0;
+	{value,{Suite,GrAndCases0}} ->
+	    GrAndCases = insert_groups2(Groups,GrAndCases0),
+	    insert_in_order({Suite,GrAndCases},Suites0);
+	false ->
+	    insert_in_order({Suite,Groups},Suites0)
+    end.
+
+insert_groups2(_Groups,all) ->
+    all;
+insert_groups2([Group={GrName,Cases}|Groups],GrAndCases) ->
+    case lists:keysearch(GrName,1,GrAndCases) of
+	{value,{GrName,all}} ->
+	    GrAndCases;
+	{value,{GrName,Cases0}} ->
+	    Cases1 = insert_in_order(Cases,Cases0),
+	    insert_groups2(Groups,insert_in_order({GrName,Cases1},GrAndCases));
+	false ->
+	    insert_groups2(Groups,insert_in_order(Group,GrAndCases))
+    end;
+insert_groups2([],GrAndCases) ->
+    GrAndCases.
+
 insert_cases(Node,Dir,Suite,Cases,Tests) when is_list(Cases) ->
     case lists:keysearch({Node,Dir},1,Tests) of
 	{value,{{Node,Dir},[{all,_}]}} ->
@@ -659,6 +878,35 @@ skip_suites(_Node,_Dir,[],_Cmt,Tests) ->
 skip_suites(Node,Dir,S,Cmt,Tests) ->
     skip_suites(Node,Dir,[S],Cmt,Tests).
 
+skip_groups(Node,Dir,Suite,Group,Case,Cmt,Tests) when is_atom(Group) ->
+    skip_groups(Node,Dir,Suite,[Group],[Case],Cmt,Tests);
+skip_groups(Node,Dir,Suite,Groups,Cases,Cmt,Tests) when
+      ((Cases == all) or is_list(Cases)) and is_list(Groups) ->
+    Suites =
+	case lists:keysearch({Node,Dir},1,Tests) of
+	    {value,{{Node,Dir},Suites0}} ->
+		Suites0;
+	    false ->
+		[]
+	end,
+    Suites1 = skip_groups1(Suite,[{Gr,Cases} || Gr <- Groups],Cmt,Suites),
+    insert_in_order({{Node,Dir},Suites1},Tests);
+skip_groups(Node,Dir,Suite,Groups,Case,Cmt,Tests) when is_atom(Case) ->
+    Cases = if Case == all -> all; true -> [Case] end,
+    skip_groups(Node,Dir,Suite,Groups,Cases,Cmt,Tests).
+
+skip_groups1(Suite,Groups,Cmt,Suites0) ->
+    SkipGroups = lists:map(fun(Group) ->
+				   {Group,{skip,Cmt}}
+			   end,Groups),
+    case lists:keysearch(Suite,1,Suites0) of
+	{value,{Suite,GrAndCases0}} ->
+	    GrAndCases1 = GrAndCases0 ++ SkipGroups,
+	    insert_in_order({Suite,GrAndCases1},Suites0);
+	false ->
+	    insert_in_order({Suite,SkipGroups},Suites0)
+    end.
+
 skip_cases(Node,Dir,Suite,Cases,Cmt,Tests) when is_list(Cases) ->
     Suites =
 	case lists:keysearch({Node,Dir},1,Tests) of
@@ -753,6 +1001,8 @@ valid_terms() ->
      {cover,3},
      {config,2},
      {config,3},
+     {userconfig, 2},
+     {userconfig, 3},
      {alias,3},
      {logdir,2},
      {logdir,3},
@@ -761,7 +1011,6 @@ valid_terms() ->
      {event_handler,4},
      {include,2},
      {include,3},
-
      {suites,3},
      {suites,4},
      {cases,4},
@@ -816,7 +1065,3 @@ common_letters([L|Ls],Term,Count) ->
     end;
 common_letters([],_,Count) -> 
     Count.
-
-
-    
-