feat: use mongodb official driver instead of mgo (#1782)

* wip: backup

* wip: backup

* wip: backup

* backup

* backup

* backup

* add more tests

* fix wrong dependency

* fix lint errors

* remove test due to data race

* add tests

* fix test error

* add mon.Model

* add mon.Model unmarshal

* add monc

* add more tests for monc

* add more tests for monc

* add docs for mon and monc packages

* fix doc errors

* chhore: add comment

* chore: fix test bug

* chore: refine tests

* chore: remove primitive.NewObjectID in test code

* chore: rename test files for typo

core/stores/mongo/util_test.go

@@ -0,0 +1,35 @@
+package mongo
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatAddrs(t *testing.T) {
+	tests := []struct {
+		addrs  []string
+		expect string
+	}{
+		{
+			addrs:  []string{"a", "b"},
+			expect: "a,b",
+		},
+		{
+			addrs:  []string{"a", "b", "c"},
+			expect: "a,b,c",
+		},
+		{
+			addrs:  []string{},
+			expect: "",
+		},
+		{
+			addrs:  nil,
+			expect: "",
+		},
+	}
+
+	for _, test := range tests {
+		assert.Equal(t, test.expect, FormatAddr(test.addrs))
+	}
+}