Another attempt at fixing the flaky ddoc_cache test

This test has been the most flaky one lately.

DDoc cache does quite a bit async process spawning. It's possible that entry
processes never finish opening before the test already proceeds and expects all
10 entries to be removed.

Also, to increase isolation between tests switch eunit `setup` to `foreach`.
This will restart the whole ddoc app and reduce possible influence of one test
on another.

Fix: #4793

src/ddoc_cache/test/eunit/ddoc_cache_lru_test.erl

@@ -57,16 +57,16 @@ check_not_started_test() ->
 
 check_lru_test_() ->
     {
-        setup,
+        foreach,
         fun start_couch/0,
         fun stop_couch/1,
-        with([
-            ?TDEF(check_multi_start, 10),
-            ?TDEF(check_multi_open, 10),
-            ?TDEF(check_capped_size, 10),
-            ?TDEF(check_cache_refill, 10),
-            ?TDEF(check_evict_and_exit, 10)
-        ])
+        [
+            ?TDEF_FE(check_multi_start, 10),
+            ?TDEF_FE(check_multi_open, 10),
+            ?TDEF_FE(check_capped_size, 10),
+            ?TDEF_FE(check_cache_refill, 10),
+            ?TDEF_FE(check_evict_and_exit, 10)
+        ]
     }.
 
 check_multi_start(_) ->
@@ -200,10 +200,23 @@ check_cache_refill({DbName, _}) ->
         lists:seq(1, 5)
     ),
 
+    % Wait for all 10 entries (5 ddocid + 5 ddocid_rev) to be inserted into the
+    % LRU before proceeding
+    test_util:wait(
+        fun() ->
+            case ets:info(?LRU, size) of
+                10 -> ok;
+                _ -> wait
+            end
+        end
+    ),
+
     ShardName = mem3:name(hd(mem3:shards(DbName))),
     {ok, _} = ddoc_cache_lru:handle_db_event(ShardName, deleted, foo),
     meck:wait(ddoc_cache_ev, event, [evicted, DbName], ?EVENT_TIMEOUT),
-    meck:wait(10, ddoc_cache_ev, event, [removed, '_'], ?EVENT_TIMEOUT),
+    % We're waiting for 5 ddocid and 5 ddocid_rev entries to be removed
+    % Use a longer wait timeout as we expect 10 calls instead of just 1
+    meck:wait(10, ddoc_cache_ev, event, [removed, '_'], 5 * ?EVENT_TIMEOUT),
     test_util:wait(
         fun() ->
             case ets:info(?CACHE, size) of