Add Integration Testing for issue #40868 (#40972)

* Integration tests for hunger and thirst

* Adjustements after the code review comments

* cleanup

---------

Co-authored-by: slarticodefast <161409025+slarticodefast@users.noreply.github.com>

Content.IntegrationTests/Tests/Nutrition/HungerThirstTest.cs

@@ -0,0 +1,97 @@
+using Content.IntegrationTests.Tests.Interaction;
+using Content.Shared.Chemistry.Components;
+using Content.Shared.Nutrition.Components;
+using Content.Shared.Nutrition.EntitySystems;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Prototypes;
+
+namespace Content.IntegrationTests.Tests.Nutrition;
+
+/// <summary>
+/// Tests the mechanics of hunger and thirst.
+/// </summary>
+public sealed class HungerThirstTest : InteractionTest
+{
+    private readonly EntProtoId _drink = "DrinkLemonadeGlass";
+    private readonly EntProtoId _food = "FoodCakeVanillaSlice";
+    protected override string PlayerPrototype => "MobHuman";
+
+    /// <summary>
+    /// Tests that hunger and thirst values decrease over time (low means hungrier and thirstier).
+    /// Tests that hunger and thirst values increase when eating/drinking (high means less hungry and thirsty).
+    /// </summary>
+    [Test]
+    public async Task HungerThirstIncreaseDecreaseTest()
+    {
+        // Ensure that the player can breathe and not suffocate
+        await AddAtmosphere();
+
+        var hungerComponent = Comp<HungerComponent>(Player);
+        var thirstComponent = Comp<ThirstComponent>(Player);
+        var hungerSystem = SEntMan.System<HungerSystem>();
+        var thirstSystem = SEntMan.System<ThirstSystem>();
+        var ingestionSystem = SEntMan.System<IngestionSystem>();
+
+        // Set initial value
+        hungerSystem.SetHunger(SPlayer, hungerComponent.Thresholds[HungerThreshold.Okay], hungerComponent);
+        thirstSystem.SetThirst(SPlayer, thirstComponent, thirstComponent.ThirstThresholds[ThirstThreshold.Okay]);
+
+        // Ensure hunger and thirst value decrease over time (the Urist gets hungrier/thirstier)
+        var previousHungerValue = hungerSystem.GetHunger(hungerComponent);
+        var previousThirstValue = thirstComponent.CurrentThirst; // TODO: combined sation system with a sane API
+
+        // Simulate long enough for both update loops to run
+        var runTime = Math.Max((float)hungerComponent.ThresholdUpdateRate.TotalSeconds, (float)thirstComponent.UpdateRate.TotalSeconds) + 1f;
+        await RunSeconds(runTime);
+
+        var currentHungerValue = hungerSystem.GetHunger(hungerComponent);
+        Assert.That(currentHungerValue, Is.LessThan(previousHungerValue), "Hunger value did not decrease over time");
+        previousHungerValue = currentHungerValue;
+
+        var currentThirstValue = thirstComponent.CurrentThirst;
+        Assert.That(currentThirstValue, Is.LessThan(previousThirstValue), "Thirst value did not decrease over time");
+        previousThirstValue = currentThirstValue;
+
+        // Now we spawn food in the Urist's hand
+        await PlaceInHands(_food);
+
+        // We eat the food in hand
+        await UseInHand();
+
+        // To see a change in hunger, we need to wait at least 30 seconds
+        await RunSeconds(30);
+
+        // We ensure the food is fully eaten
+        var foodEaten = HandSys.GetActiveItem((SPlayer, Hands));
+        Assert.That(foodEaten, Is.Null, "Food item did not disappear after eating it");
+
+        // Ensure that the hunger value has increased (The Urist is less hungry)
+        Assert.That(hungerSystem.GetHunger(hungerComponent), Is.GreaterThan(previousHungerValue), "Hunger value did not increase after eating food");
+
+        // Now we spawn a drink in the Urist's hand
+        var drink = await PlaceInHands(_drink);
+
+        // Get the solution that can be consumed
+        Assert.That(ingestionSystem.CanConsume(SPlayer, SPlayer, ToServer(drink), out var solution, out _),
+            "Unable to get the solution or the entity can not be consumed");
+
+        // Find the initial amount of solution in the drink
+        var initialSolutionVolume = solution.Value.Comp.Solution.Volume;
+
+        // We drink the drink in hand
+        await UseInHand();
+
+        // To see a change in thirst, we need to wait at least 30 seconds
+        await RunSeconds(30);
+
+        // Ensure the solution volume has decreased
+        Assert.That(solution.Value.Comp.Solution.Volume, Is.LessThan(initialSolutionVolume), "Solution volume did not decrease after drinking");
+
+        // Ensure that the thirst value has increased (The Urist is less thirsty)
+        Assert.That(thirstComponent.CurrentThirst, Is.GreaterThan(previousThirstValue), "Thirst value did not increase after drinking");
+
+        // Make sure that the glass did not get deleted after drinking from it
+        var glass = HandSys.GetActiveItem((SPlayer, Hands));
+        Assert.That(glass, Is.Not.Null, "Glass got deleted after drinking from it");
+    }
+}