test: rework flaky vshard strategy test cases

Before this patch, retry in vshard call resulted in test fail since
each case expects the exact count of API calls. It often had failed in
repository CI and tarantool/tarantool integration CI (see [1], for
example).

1. https://github.com/tarantool/tarantool/actions/runs/4222968119/attempts/6

Author: DifferentialOrange

test/integration/read_calls_strategies_test.lua

@@ -44,8 +44,21 @@ pgroup.before_all(function(g)
         g.cluster.main_server.net_box:call('clear_vshard_calls')
     end
 
-    g.get_vshard_calls = function()
-        return g.cluster.main_server.net_box:eval('return _G.vshard_calls')
+    g.get_vshard_call_strategies = function()
+        -- Retries are possible, especially in CI, so we don't assert
+        -- the quantity of calls, only strategies used.
+        local vshard_calls = g.cluster.main_server.net_box:eval('return _G.vshard_calls')
+
+        local vshard_call_strategies_map = {}
+        for _, v in ipairs(vshard_calls) do
+            vshard_call_strategies_map[v] = true
+        end
+
+        local vshard_call_strategies = {}
+        for k, _ in pairs(vshard_call_strategies_map) do
+            table.insert(vshard_call_strategies, k)
+        end
+        return vshard_call_strategies
     end
 
     -- patch vshard.router.call* functions
@@ -69,8 +82,8 @@ pgroup.test_get = function(g)
         prefer_replica = g.params.prefer_replica
     }})
     t.assert_equals(err, nil)
-    local vshard_calls = g.get_vshard_calls('call_single_impl')
-    t.assert_equals(vshard_calls, {g.params.exp_vshard_call})
+    local vshard_call_strategies = g.get_vshard_call_strategies('call_single_impl')
+    t.assert_equals(vshard_call_strategies, {g.params.exp_vshard_call})
 end
 
 pgroup.test_select = function(g)
@@ -82,8 +95,8 @@ pgroup.test_select = function(g)
         fullscan = true
     }})
     t.assert_equals(err, nil)
-    local vshard_calls = g.get_vshard_calls('call_impl')
-    t.assert_equals(vshard_calls, {g.params.exp_vshard_call, g.params.exp_vshard_call})
+    local vshard_call_strategies = g.get_vshard_call_strategies('call_impl')
+    t.assert_equals(vshard_call_strategies, {g.params.exp_vshard_call})
 end
 
 pgroup.test_pairs = function(g)
@@ -102,8 +115,8 @@ pgroup.test_pairs = function(g)
         for _, _ in crud.pairs('customers', nil, opts) do end
     ]], {opts})
     t.assert_equals(err, nil)
-    local vshard_calls = g.get_vshard_calls('call_impl')
-    t.assert_equals(vshard_calls, {g.params.exp_vshard_call, g.params.exp_vshard_call})
+    local vshard_call_strategies = g.get_vshard_call_strategies('call_impl')
+    t.assert_equals(vshard_call_strategies, {g.params.exp_vshard_call})
 end
 
 pgroup.test_count = function(g)
@@ -115,6 +128,6 @@ pgroup.test_count = function(g)
         fullscan = true
     }})
     t.assert_equals(err, nil)
-    local vshard_calls = g.get_vshard_calls('call_impl')
-    t.assert_equals(vshard_calls, {g.params.exp_vshard_call, g.params.exp_vshard_call})
+    local vshard_call_strategies = g.get_vshard_call_strategies('call_impl')
+    t.assert_equals(vshard_call_strategies, {g.params.exp_vshard_call})
 end