diff --git a/build.sbt b/build.sbt
index 9bb3bfacd9be5..b04b3ac441bf8 100644
--- a/build.sbt
+++ b/build.sbt
@@ -154,7 +154,7 @@ lazy val common = module("common",
 
 lazy val rating = module("rating",
   Seq(common, db, memo, i18n),
-  reactivemongo.bundle
+  reactivemongo.bundle ++ specs2.bundle 
 )
 
 lazy val perfStat = module("perfStat",
diff --git a/modules/rating/src/test/RatingCalculatorTest.scala b/modules/rating/src/test/RatingCalculatorTest.scala
new file mode 100644
index 0000000000000..6f565488b0404
--- /dev/null
+++ b/modules/rating/src/test/RatingCalculatorTest.scala
@@ -0,0 +1,148 @@
+package lila.rating
+
+import org.specs2.mutable.Specification
+import org.goochjs.glicko2.*
+import chess.{ Color, White, Black }
+
+class RatingCalculatorTest extends Specification {
+
+  def updateRatings(wRating: Rating, bRating: Rating, winner: Option[Color]) =
+    val result = winner match
+      case Some(chess.White) => Glicko.Result.Win
+      case Some(chess.Black) => Glicko.Result.Loss
+      case None              => Glicko.Result.Draw
+    val results = new GameRatingPeriodResults()
+    result match
+      case Glicko.Result.Draw => results.addDraw(wRating, bRating)
+      case Glicko.Result.Win  => results.addWin(wRating, bRating)
+      case Glicko.Result.Loss => results.addWin(bRating, wRating)
+    Glicko.system.updateRatings(results, true)
+
+  "compute rating" in {
+    "default deviation" in {
+      "white wins" in {
+        val wr = Perf.default.toRating
+        val br = Perf.default.toRating
+        updateRatings(wr, br, White.some)
+        wr.getRating must beCloseTo(1741d, 1d)
+        br.getRating must beCloseTo(1258d, 1d)
+        wr.getRatingDeviation must beCloseTo(396d, 1d)
+        br.getRatingDeviation must beCloseTo(396d, 1d)
+        wr.getVolatility must beCloseTo(0.08999, 0.00001d)
+        br.getVolatility must beCloseTo(0.08999, 0.00001d)
+      }
+      "black wins" in {
+        val wr = Perf.default.toRating
+        val br = Perf.default.toRating
+        updateRatings(wr, br, Black.some)
+        wr.getRating must beCloseTo(1258d, 1d)
+        br.getRating must beCloseTo(1741d, 1d)
+        wr.getRatingDeviation must beCloseTo(396d, 1d)
+        br.getRatingDeviation must beCloseTo(396d, 1d)
+        wr.getVolatility must beCloseTo(0.08999, 0.00001d)
+        br.getVolatility must beCloseTo(0.08999, 0.00001d)
+      }
+      "draw" in {
+        val wr = Perf.default.toRating
+        val br = Perf.default.toRating
+        updateRatings(wr, br, None)
+        wr.getRating must beCloseTo(1500d, 1d)
+        br.getRating must beCloseTo(1500d, 1d)
+        wr.getRatingDeviation must beCloseTo(396d, 1d)
+        br.getRatingDeviation must beCloseTo(396d, 1d)
+        wr.getVolatility must beCloseTo(0.08999, 0.00001d)
+        br.getVolatility must beCloseTo(0.08999, 0.00001d)
+      }
+    }
+    "low deviation" in {
+      val perf = Perf.default.copy(glicko =
+        Glicko.default.copy(
+          deviation = 80,
+          volatility = 0.06
+        )
+      )
+      "white wins" in {
+        val wr = perf.toRating
+        val br = perf.toRating
+        updateRatings(wr, br, White.some)
+        wr.getRating must beCloseTo(1517d, 1d)
+        br.getRating must beCloseTo(1482d, 1d)
+        wr.getRatingDeviation must beCloseTo(78d, 1d)
+        br.getRatingDeviation must beCloseTo(78d, 1d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.06, 0.00001d)
+      }
+      "black wins" in {
+        val wr = perf.toRating
+        val br = perf.toRating
+        updateRatings(wr, br, Black.some)
+        wr.getRating must beCloseTo(1482d, 1d)
+        br.getRating must beCloseTo(1517d, 1d)
+        wr.getRatingDeviation must beCloseTo(78d, 1d)
+        br.getRatingDeviation must beCloseTo(78d, 1d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.06, 0.00001d)
+      }
+      "draw" in {
+        val wr = perf.toRating
+        val br = perf.toRating
+        updateRatings(wr, br, None)
+        wr.getRating must beCloseTo(1500d, 1d)
+        br.getRating must beCloseTo(1500d, 1d)
+        wr.getRatingDeviation must beCloseTo(78d, 1d)
+        br.getRatingDeviation must beCloseTo(78d, 1d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.06, 0.00001d)
+      }
+    }
+    "mixed ratings and deviations" in {
+      val wP = Perf.default.copy(glicko =
+        Glicko.default.copy(
+          rating = 1400,
+          deviation = 79,
+          volatility = 0.06
+        )
+      )
+      val bP = Perf.default.copy(glicko =
+        Glicko.default.copy(
+          rating = 1550,
+          deviation = 110,
+          volatility = 0.065
+        )
+      )
+      "white wins" in {
+        val wr = wP.toRating
+        val br = bP.toRating
+        updateRatings(wr, br, White.some)
+        wr.getRating must beCloseTo(1422d, 1d)
+        br.getRating must beCloseTo(1506d, 1d)
+        wr.getRatingDeviation must beCloseTo(77d, 1d)
+        br.getRatingDeviation must beCloseTo(105d, 1d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.065, 0.00001d)
+      }
+      "black wins" in {
+        val wr = wP.toRating
+        val br = bP.toRating
+        updateRatings(wr, br, Black.some)
+        wr.getRating must beCloseTo(1389d, 1d)
+        br.getRating must beCloseTo(1568d, 1d)
+        wr.getRatingDeviation must beCloseTo(78d, 1d)
+        br.getRatingDeviation must beCloseTo(105d, 1d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.065, 0.00001d)
+      }
+      "draw" in {
+        val wr = wP.toRating
+        val br = bP.toRating
+        updateRatings(wr, br, None)
+        wr.getRating must beCloseTo(1406d, 1d)
+        br.getRating must beCloseTo(1537d, 1d)
+        wr.getRatingDeviation must beCloseTo(78d, 1d)
+        br.getRatingDeviation must beCloseTo(105.87d, 0.01d)
+        wr.getVolatility must beCloseTo(0.06, 0.00001d)
+        br.getVolatility must beCloseTo(0.065, 0.00001d)
+      }
+    }
+  }
+}