From 03da5e0be061dfed832ca7eaaf5998fa7cf27640 Mon Sep 17 00:00:00 2001
From: Andrew Thompson <andrew@hijacked.us>
Date: Wed, 5 Feb 2014 14:41:25 -0500
Subject: [PATCH 1/2] Add random_suite_order option to eunit command

Option takes either 'true' or a numeric seed value. If true is passed, a
random seed is generated and used. The numeric seed value is for
repeatability.

The idea here is to root out test suites that are order dependant, or
that fail in the presence of certain orderings.
---
 src/rebar_eunit.erl | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/rebar_eunit.erl b/src/rebar_eunit.erl
index e04b28e..323e199 100644
--- a/src/rebar_eunit.erl
+++ b/src/rebar_eunit.erl
@@ -150,7 +150,7 @@ run_eunit(Config, CodePath, SrcErls) ->
                         AllBeamFiles),
     OtherBeamFiles = TestBeamFiles --
         [filename:rootname(N) ++ "_tests.beam" || N <- AllBeamFiles],
-    ModuleBeamFiles = BeamFiles ++ OtherBeamFiles,
+    ModuleBeamFiles = randomize_suites(Config, BeamFiles ++ OtherBeamFiles),
 
     %% Get modules to be run in eunit
     AllModules = [rebar_utils:beam_to_mod(?EUNIT_DIR, N) || N <- AllBeamFiles],
@@ -233,6 +233,33 @@ get_suites(Config) ->
             Suites
     end.
 
+%%
+%% == randomize suites ==
+%%
+
+randomize_suites(Config, Modules) ->
+    case rebar_config:get_global(Config, random_suite_order, undefined) of
+        undefined ->
+            Modules;
+        "true" ->
+            Seed = crypto:rand_uniform(1, 65535),
+            randomize_suites1(Modules, Seed);
+        String ->
+            try list_to_integer(String) of
+                Seed ->
+                    randomize_suites1(Modules, Seed)
+            catch
+                error:badarg ->
+                    ?ERROR("Bad random seed provided: ~p~n", [String]),
+                    ?FAIL
+            end
+    end.
+
+randomize_suites1(Modules, Seed) ->
+    random:seed(35, Seed, 1337),
+    ?CONSOLE("Randomizing suite order with seed ~b~n", [Seed]),
+    [X||{_,X} <- lists:sort([{random:uniform(), M} || M <- Modules])].
+
 %%
 %% == get matching tests ==
 %%

From 2f6991cbd7ae249e0d24f991c37b2746fd78b1d6 Mon Sep 17 00:00:00 2001
From: Andrew Thompson <andrew@hijacked.us>
Date: Thu, 6 Feb 2014 14:58:38 -0500
Subject: [PATCH 2/2] Add documentation

---
 src/rebar.erl       | 2 ++
 src/rebar_eunit.erl | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/src/rebar.erl b/src/rebar.erl
index b213e6c..833e397 100644
--- a/src/rebar.erl
+++ b/src/rebar.erl
@@ -369,6 +369,8 @@ eunit       [suite[s]=foo]               Run eunit tests in foo.erl and
                                          no such test exists, run the test whose
                                          name starts with bar in the suite's
                                          _tests module
+            [random_suite_order=true]    Run tests in a random order, either with
+            [random_suite_order=Seed]    a random seed for the PRNG, or a specific one.
 
 ct          [suite[s]=] [case=]          Run common_test suites
 
diff --git a/src/rebar_eunit.erl b/src/rebar_eunit.erl
index 323e199..3fe1280 100644
--- a/src/rebar_eunit.erl
+++ b/src/rebar_eunit.erl
@@ -126,6 +126,9 @@ info_help(Description) ->
        "               name starts with bar and, if no such test exists,~n"
        "               run the test whose name starts with bar in the~n"
        "               suite's _tests module)~n"
+       "  random_suite_order=true (Run tests in random order)~n"
+       "  random_suite_order=Seed (Run tests in random order,~n"
+       "                           with the PRNG seeded with Seed)~n"
        "  compile_only=true (Compile but do not run tests)",
        [
         Description,