Add total number of gases atmospherics test (#1639)

Content.IntegrationTests/Tests/Atmos/ConstantsTest.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Linq;
+using Content.Shared.Atmos;
+using NUnit.Framework;
+
+namespace Content.IntegrationTests.Tests.Atmos
+{
+    [TestFixture]
+    [TestOf(typeof(Atmospherics))]
+    public class ConstantsTest : ContentIntegrationTest
+    {
+        [Test]
+        public void TotalGasesTest()
+        {
+            var server = StartServerDummyTicker();
+
+            server.Post(() =>
+            {
+                Assert.That(Atmospherics.Gases.Count(), Is.EqualTo(Atmospherics.TotalNumberOfGases));
+
+                Assert.That(Enum.GetValues(typeof(Gas)).Length, Is.EqualTo(Atmospherics.TotalNumberOfGases));
+            });
+        }
+    }
+}