Mongodb query using mgov2

I have a collection of endpoint point tests conducted on various channels. A sample document from the collection is:

{
    "_id" : ObjectId("59959b30c699811077751b12"),
    "teststatus" : "Fail",
    "channelname" : "HouseController",
    "timestamp" : ISODate("2017-08-17T13:15:53.170Z"),
    "testid" : "llpKIgIfiiquqkSApwNn"
}

I am querying this to project the result something like this:

[
  {
    "Fail": 20,
    "Success Count": 30,
    "Total": 50,
    "channel": "c3"
  }, ...

But I am getting the wrong count for success and fail rate. My current query in golang looks like:

o1:=  bson.M{
	"$project" :bson.M{
		"channel": "$channelname",
		"time":"$timestamp",
		"teststatus" : "$teststatus",
		"_id":1,
	},
}
o2:=  bson.M{
	"$group" :bson.M{
		"_id": "$channel",
		"Success": bson.M{
			"$sum":bson.M{ "$eq" :"teststatus","Pass"},
		},
		"Total": bson.M{
			"$sum": 1,
		},
	},
}
o3:=  bson.M{
	"$project" :bson.M{
		"channel": "$_id",
		"Success Count":"$Success",
		"Total" : "$Total",
		"_id":0,
		"Fail": bson.M{
			"$subtract": []interface{}{"$Total", "$Success"},
		},
	},
}

I am doing wrong in the counting of success count. I just cant figure to do it right. I have just started with mgo and golang.

Thanks in advance

You need to use $cond to do conditional counting. For example the following counts all tests, failed ones and successful ones in one step:

o2 := bson.M{
    "$group" :bson.M{
        "_id": "$channel",
        "Total": bson.M{
            "$sum": 1,
        },
        "Success": bson.M{"$sum": bson.M{
            "$cond": []interface{}{
                bson.M{ "$eq": []interface{}{"$teststatus", "Pass"}},
                1, 0,
            },
        }},
        "Fail": bson.M{"$sum": bson.M{
            "$cond": []interface{}{
                bson.M{"$eq": []interface{}{"$teststatus", "Fail"}},
                1, 0,
            },
        }},
    },
}