Fix ratio issues on SlipSolution

Content.Shared/Chemistry/Solution.cs

@@ -181,11 +181,13 @@ namespace Content.Shared.Chemistry
 
             newSolution = new Solution();
             var newTotalVolume = ReagentUnit.New(0M);
-            var ratio = (TotalVolume - quantity).Decimal() / TotalVolume.Decimal();
+            var remainingVolume = TotalVolume;
 
             for (var i = 0; i < _contents.Count; i++)
             {
                 var reagent = _contents[i];
+                var ratio = (remainingVolume - quantity).Decimal() / remainingVolume.Decimal();
+                remainingVolume -= reagent.Quantity;
 
                 var newQuantity = reagent.Quantity * ratio;
                 var splitQuantity = reagent.Quantity - newQuantity;
@@ -193,10 +195,11 @@ namespace Content.Shared.Chemistry
                 _contents[i] = new ReagentQuantity(reagent.ReagentId, newQuantity);
                 newSolution._contents.Add(new ReagentQuantity(reagent.ReagentId, splitQuantity));
                 newTotalVolume += splitQuantity;
+                quantity -= splitQuantity;
             }
 
-            TotalVolume = TotalVolume * ratio;
             newSolution.TotalVolume = newTotalVolume;
+            TotalVolume -= newTotalVolume;
 
             return newSolution;
         }

Content.Tests/Shared/Chemistry/Solution_Tests.cs

@@ -255,7 +255,25 @@ namespace Content.Tests.Shared.Chemistry
             Assert.That(splitSolution.GetReagentQuantity("water").Float(), Is.EqualTo(reduce));
             Assert.That(splitSolution.TotalVolume.Float(), Is.EqualTo(reduce));
         }
-        
+
+        [Test]
+        [TestCase(2)]
+        [TestCase(10)]
+        [TestCase(100)]
+        [TestCase(1000)]
+        public void SplitRounding(int amount)
+        {
+            var solutionOne = new Solution();
+            solutionOne.AddReagent("foo", ReagentUnit.New(amount));
+            solutionOne.AddReagent("bar", ReagentUnit.New(amount));
+            solutionOne.AddReagent("baz", ReagentUnit.New(amount));
+
+            var splitAmount = ReagentUnit.New(5);
+            var split = solutionOne.SplitSolution(splitAmount);
+
+            Assert.That(split.TotalVolume, Is.EqualTo(splitAmount));
+        }
+
         [Test]
         public void SplitSolutionMoreThanTotalRemovesAll()
         {