Add reagent dispenser BUI test (#15443)

Content.IntegrationTests/Tests/Chemistry/DispenserTest.cs

@@ -0,0 +1,35 @@
+using System.Threading.Tasks;
+using Content.IntegrationTests.Tests.Interaction;
+using Content.Shared.Chemistry;
+using Content.Shared.Containers.ItemSlots;
+using NUnit.Framework;
+
+namespace Content.IntegrationTests.Tests.Chemistry;
+
+public sealed class DispenserTest : InteractionTest
+{
+    /// <summary>
+    ///     Basic test that checks that a beaker can be inserted and ejected from a dispenser.
+    /// </summary>
+    [Test]
+    public async Task InsertEjectBuiTest()
+    {
+        await SpawnTarget("chem_dispenser");
+        ToggleNeedPower();
+
+        // Insert beaker
+        await Interact("Beaker");
+        Assert.IsNull(Hands.ActiveHandEntity);
+
+        // Open BUI
+        await Interact("");
+
+        // Eject beaker via BUI.
+        var ev = new ItemSlotButtonPressedEvent(SharedChemMaster.InputSlotName);
+        await SendBui(ReagentDispenserUiKey.Key, ev);
+
+        // Beaker is back in the player's hands
+        Assert.IsNotNull(Hands.ActiveHandEntity);
+        AssertPrototype("Beaker", Hands.ActiveHandEntity);
+    }
+}