From 4f5c19c5495eaf45b45faad6bfb51de25e9ad258 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 10 May 2016 11:21:01 +0200
Subject: time_SUITE: Make consistency/1 work in any timezone

time_SUITE:consistency/1 would only work in CET, which was
reasonable when the test suites were always run in Stockholm.
Nowadays it is expected that you can run the test suite in any
timezone. Therefore, only make sure that that difference between
localtime/1 and universaltime/1 is "reasonable".
---
 erts/emulator/test/time_SUITE.erl | 77 ++++++++++-----------------------------
 1 file changed, 19 insertions(+), 58 deletions(-)

diff --git a/erts/emulator/test/time_SUITE.erl b/erts/emulator/test/time_SUITE.erl
index 76d440529f..87b8c62cfa 100644
--- a/erts/emulator/test/time_SUITE.erl
+++ b/erts/emulator/test/time_SUITE.erl
@@ -209,23 +209,17 @@ test_seconds_to_univ([]) ->
 
 
 %% Test that the the different time functions return
-%% consistent results. (See the test case for assumptions
-%% and limitations.)
-consistency(Config) when is_list(Config) ->
-    %% Test the following equations:
-    %% 		date() & time() == erlang:localtime()
-    %% 		erlang:universaltime() + timezone == erlang:localtime()
+%% consistent results.
+consistency(_Config) ->
+    %% Test that:
+    %% 	 * date() & time() gives the same time as erlang:localtime()
     %%
-    %% Assumptions:
-    %% 		Middle-European time zone, EU rules for daylight-saving time.
-    %%
-    %% Limitations:
-    %% 		Localtime and universaltime must be in the same	month.
-    %%	        Daylight-saving calculations are incorrect from the last
-    %%		Sunday of March and October to the end of the month.
+    %%   * the difference between erlang:universaltime() and
+    %%     erlang:localtime() is reasonable (with assuming any
+    %%     particular timezone)
 
     ok = compare_date_time_and_localtime(16),
-    ok = compare_local_and_universal(16).
+    compare_local_and_universal(16).
 
 compare_date_time_and_localtime(Times) when Times > 0 ->
     {Year, Mon, Day} = date(),
@@ -238,22 +232,18 @@ compare_date_time_and_localtime(0) ->
     error.
 
 compare_local_and_universal(Times) when Times > 0 ->
-    case compare(erlang:universaltime(), erlang:localtime()) of
-	true -> ok;
-	false -> compare_local_and_universal(Times-1)
-    end;
-compare_local_and_universal(0) ->
-    error.
+    Utc = erlang:universaltime(),
+    Local = erlang:localtime(),
+    io:format("local = ~p, utc = ~p", [Local,Utc]),
 
-compare(Utc0, Local) ->
-    io:format("local = ~p, utc = ~p", [Local, Utc0]),
-    Utc = linear_time(Utc0)+effective_timezone(Utc0)*3600,
-    case linear_time(Local) of
-	Utc -> true;
-	Other ->
-	    io:format("Failed: local = ~p, utc = ~p~n",
-		      [Other, Utc]),
-	    false
+    AcceptableDiff = 14*3600,
+    case linear_time(Utc) - linear_time(Local) of
+	Diff when abs(Diff) < AcceptableDiff ->
+	    ok;
+	Diff ->
+	    io:format("More than ~p seconds difference betwen "
+		      "local and universal time", [Diff]),
+	    ct:fail(huge_diff)
     end.
 
 %% This function converts a date and time to a linear time.
@@ -280,35 +270,6 @@ days_in_february(Year) ->
 	_ -> 28
     end.
 
-%% This functions returns either the normal timezone or the
-%% the DST timezone, depending on the given UTC time.
-%%
-%% XXX This function uses an approximation of the EU rule for
-%% daylight saving time.  This function will fail in the
-%% following intervals: After the last Sunday in March upto
-%% the end of March, and after the last Sunday in October
-%% upto the end of October.
-
-effective_timezone(Time) ->
-    case os:type() of
-	{unix,_} ->
-	    case os:cmd("date '+%Z'") of
-		"SAST"++_ ->
-		    2;
-		_ ->
-		    effective_timezone1(Time)
-	    end;
-	_ ->
-	    effective_timezone1(Time)
-    end.
-
-effective_timezone1({{_Year,Mon,_Day}, _}) when Mon < 4 ->
-    ?timezone;
-effective_timezone1({{_Year,Mon,_Day}, _}) when Mon > 10 ->
-    ?timezone;
-effective_timezone1(_) ->
-    ?dst_timezone.
-
 %% Test (the bif) os:timestamp/0, which is something quite like, but not
 %% similar to erlang:now...
 
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