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[edit] Authors

Rudolph van Graan

[edit] Debugging

Sometimes one needs to debug a particular section of code and see functions being called and their parameters and return values. In Erlang you use [ tracing]

Using our test case from Testing with Test Helper, we modify it with a configuration case that enables basic function tracing:

tracing_start(doc) ->
  ["Starts tracing on test_case"];
tracing_start(suite) ->
  [];
tracing_start(Config) ->
  debughelper:start(),
  debughelper:trace(?MODULE,test_case),
  Config.

and adds it to our all(...) test case:

all(suite) -> 
  [{conf,
    tracing_start,[test_case_2],
    tracing_stop}].

The intention here is to see what test_case_3 does.

Here is the output of test case 3:

====================Start of Test test_case_3======================
(<0.220.0>) call simple_test_SUITE:test_case_3(suite)
(<0.220.0>) returned from simple_test_SUITE:test_case_3/1 -> []
This is test 3!
(<0.220.0>) call simple_test_SUITE:test_case_3([{data_dir,"/Users/rvg/svn/modules/common/test/simple_test_SUITE_data/"},
 {priv_dir,"/Users/rvg/svn/modules/common/test/simple_test_SUITE_priv/"}])
Function 1!
Function 2!

====================End of Test test_case_3========================
(<0.220.0>) returned from simple_test_SUITE:test_case_3/1 -> ok

How do we read this?

(<0.220.0>) call simple_test_SUITE:test_case_3(suite) 
(<0.220.0>) returned from simple_test_SUITE:test_case_3/1 -> []

This is the call into test_case_3 that testhelper makes to determine of the test has sub tests. We can see that there are none, based on the empty list return.

Here testhelper runs our test:

(<0.220.0>) call simple_test_SUITE:test_case_3([{data_dir,"/Users/rvg/svn/modules/common/test/simple_test_SUITE_data/"},
 {priv_dir,"/Users/rvg/svn/modules/common/test/simple_test_SUITE_priv/"}])
(<0.220.0>) returned from simple_test_SUITE:test_case_3/1 -> ok

You can see that erlang should us the call into test_case_3 and that it returned the Atom ok.

[edit] debughelper.erl

Here is the code for debughelper.erl. As you can see, it is simply a wrapper around dbg, but it makes it easy and programmers don't have to remember anything about Match Specifications.

%%% Author  : Rudolph van Graan <>
%%% Description :
%%% Created : 25 Jul 2006 by Rudolph van Graan <>

-module(debughelper).

-export([start/0,
         trace/1,
         trace/2]).

start() ->
  dbg:tracer(),
  dbg:p(all,[c,sos,sol]).

trace(ModuleName) ->
  dbg:tpl(ModuleName,[{'_',[],[{message,{return_trace}}]}]).

trace(ModuleName,Function) ->
  dbg:tpl(ModuleName,Function,[{'_',[],[{message,{return_trace}}]}]).

[edit] See Also

• Match specifications
• dbg module]