Fix ScaleSolution() (#13630)

Content.Shared/Chemistry/Components/Solution.cs

@@ -317,7 +317,7 @@ namespace Content.Shared.Chemistry.Components
             if (scale == 1)
                 return;
 
-            if (scale == 0)
+            if (scale <= 0)
             {
                 RemoveAllSolution();
                 return;
@@ -326,7 +326,7 @@ namespace Content.Shared.Chemistry.Components
             _heatCapacity *= scale;
             Volume *= scale;
 
-            for (int i = 0; i <= Contents.Count; i++)
+            for (int i = 0; i < Contents.Count; i++)
             {
                 var old = Contents[i];
                 Contents[i] = new ReagentQuantity(old.ReagentId, old.Quantity * scale);

Content.Tests/Shared/Chemistry/Solution_Tests.cs

@@ -3,6 +3,7 @@ using Content.Shared.FixedPoint;
 using Robust.Shared.IoC;
 using Robust.Shared.Prototypes;
 using NUnit.Framework;
+using Robust.Shared.Utility;
 
 namespace Content.Tests.Shared.Chemistry;
 
@@ -25,6 +26,51 @@ public sealed class Solution_Tests : ContentUnitTest
         Assert.That(quantity.Int(), Is.EqualTo(1000));
     }
 
+    [Test]
+    public void ScaleSolution()
+    {
+        var solution = new Solution();
+        solution.AddReagent("water", FixedPoint2.New(20));
+        solution.AddReagent("fire", FixedPoint2.New(30));
+
+        // Test integer scaling
+        {
+            var tmp = solution.Clone();
+            tmp.ScaleSolution(0);
+            Assert.That(tmp.Contents.Count, Is.EqualTo(0));
+            Assert.That(tmp.Volume, Is.EqualTo(FixedPoint2.Zero));
+
+            tmp = solution.Clone();
+            tmp.ScaleSolution(2);
+            Assert.That(tmp.Contents.Count, Is.EqualTo(2));
+            Assert.That(tmp.Volume, Is.EqualTo(FixedPoint2.New(100)));
+            Assert.That(tmp.GetReagentQuantity("water"), Is.EqualTo(FixedPoint2.New(40)));
+            Assert.That(tmp.GetReagentQuantity("fire"), Is.EqualTo(FixedPoint2.New(60)));
+        }
+
+        // Test float scaling
+        {
+            var tmp = solution.Clone();
+            tmp.ScaleSolution(0f);
+            Assert.That(tmp.Contents.Count, Is.EqualTo(0));
+            Assert.That(tmp.Volume, Is.EqualTo(FixedPoint2.Zero));
+
+            tmp = solution.Clone();
+            tmp.ScaleSolution(2f);
+            Assert.That(tmp.Contents.Count, Is.EqualTo(2));
+            Assert.That(tmp.Volume, Is.EqualTo(FixedPoint2.New(100)));
+            Assert.That(tmp.GetReagentQuantity("water"), Is.EqualTo(FixedPoint2.New(40)));
+            Assert.That(tmp.GetReagentQuantity("fire"), Is.EqualTo(FixedPoint2.New(60)));
+
+            tmp = solution.Clone();
+            tmp.ScaleSolution(0.3f);
+            Assert.That(tmp.Contents.Count, Is.EqualTo(2));
+            Assert.That(tmp.Volume, Is.EqualTo(FixedPoint2.New(15)));
+            Assert.That(tmp.GetReagentQuantity("water"), Is.EqualTo(FixedPoint2.New(6)));
+            Assert.That(tmp.GetReagentQuantity("fire"), Is.EqualTo(FixedPoint2.New(9)));
+        }
+    }
+
     [Test]
     public void ConstructorAddReagent()
     {