diff --git a/server/src/bin/line_preview.rs b/server/src/bin/line_preview.rs
index d6a93955b..5555923cf 100644
--- a/server/src/bin/line_preview.rs
+++ b/server/src/bin/line_preview.rs
@@ -637,5 +637,6 @@ fn mood_str(m: &Mood) -> &'static str {
         Mood::Conflicted => "conflicted",
         Mood::Concerned => "concerned",
         Mood::Relieved => "relieved",
+        Mood::Focused => "focused",
     }
 }
diff --git a/server/src/content/line_pool.rs b/server/src/content/line_pool.rs
index 2078ae9b6..79524a7de 100644
--- a/server/src/content/line_pool.rs
+++ b/server/src/content/line_pool.rs
@@ -157,6 +157,7 @@ impl FromStr for Topic {
 }
 
 /// D-028 Layer 4: Mood tag — influences weighted selection.
+/// D-035 amendment (Sprint 8): `Focused` added as 9th variant.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum Mood {
     Fond,
@@ -167,6 +168,9 @@ pub enum Mood {
     Conflicted,
     Concerned,
     Relieved,
+    /// D-035 amendment (Sprint 8): task-focused NPC mood — used at The Terminal
+    /// and maintenance corridors. Maps from NpcMood::Focused.
+    Focused,
 }
 
 impl FromStr for Mood {
@@ -181,6 +185,7 @@ impl FromStr for Mood {
             "conflicted" => Ok(Self::Conflicted),
             "concerned" => Ok(Self::Concerned),
             "relieved" => Ok(Self::Relieved),
+            "focused" => Ok(Self::Focused),
             _ => Err(ParseEnumError {
                 kind: "Mood",
                 value: s.to_string(),
diff --git a/server/src/npc/mod.rs b/server/src/npc/mod.rs
index abbac1bc6..dfa65c1bf 100644
--- a/server/src/npc/mod.rs
+++ b/server/src/npc/mod.rs
@@ -2,6 +2,7 @@
 // Implements D-024: 10-axis NPC model + CombatCapability component
 // Background tier state machines for schedule, mood, relationships, job
 
+pub mod mood;
 pub mod relationships;
 pub mod routine;
 
@@ -24,8 +25,13 @@ impl Plugin for NpcPlugin {
             .init_resource::<routine::PreviousDayPhase>()
             .add_systems(
                 Update,
-                routine::check_phase_transition
-                    .before(crate::simulation::pathfinding::compute_paths),
+                (
+                    routine::check_phase_transition
+                        .before(crate::simulation::pathfinding::compute_paths),
+                    mood::update_mood
+                        .after(routine::check_phase_transition)
+                        .before(crate::simulation::dialogue::process_talk_interaction),
+                ),
             );
 
         tracing::debug!("NpcPlugin initialized");
diff --git a/server/src/npc/mood.rs b/server/src/npc/mood.rs
new file mode 100644
index 000000000..c492f478f
--- /dev/null
+++ b/server/src/npc/mood.rs
@@ -0,0 +1,669 @@
+//! NPC mood state machine (#323).
+//!
+//! Implements the 8-state NPC mood FSM (D-024 MoodState axis, D-035 taxonomy).
+//! Mood is derived each tick from simulation inputs (stress, time of day,
+//! recent interactions) and drives Layer 4 dialogue selection and monologue tone.
+//!
+//! All state transitions are deterministic — integer arithmetic only (D-010).
+//! No floats. No HashMap.
+//!
+//! ## Integration points
+//! - `ToleranceThreshold.current_stress` → primary mood driver
+//! - `SimulationTime.day_phase()` → Evening phase adds Frustrated pressure
+//! - `InteractionMemory` (Sprint 14, #325) → will set warm_active flag
+//! - `CurrentMood` (dialogue.rs) → synced each tick for Layer 4 selection
+//! - Monologue trigger system → reads NpcMood for tone selection (D-016, future)
+//! - Tell system (#337, deferred to Sprint 15) → reads MoodState
+
+use bevy_ecs::prelude::*;
+use serde::{Deserialize, Serialize};
+
+use crate::content::line_pool::Mood as ContentMood;
+use crate::npc::{Npc, ToleranceThreshold};
+use crate::simulation::dialogue::CurrentMood;
+use crate::simulation::tier::ActiveSim;
+use crate::simulation::time::{DayPhase, SimulationTime};
+
+// ---------------------------------------------------------------------------
+// NpcMood enum
+// ---------------------------------------------------------------------------
+
+/// NPC simulation mood — 8-state FSM (D-024, D-035 converged taxonomy).
+///
+/// Driven by `ToleranceThreshold` stress, time of day, and interaction events.
+/// Maps to `content::line_pool::Mood` for Layer 4 dialogue tag matching.
+///
+/// Copy team references this enum when scripting mood conditions.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default, Serialize, Deserialize)]
+pub enum NpcMood {
+    /// Default state: no notable stressors, no recent positive events.
+    #[default]
+    Neutral,
+    /// Elevated stress approaching threshold — heightened wariness.
+    Anxious,
+    /// Late-shift fatigue or repeated minor irritations.
+    Frustrated,
+    /// Low stress, positive recent context — settled and cooperative.
+    Content,
+    /// Observing unusual or off-script behavior — targeted wariness.
+    Suspicious,
+    /// Recent positive player interaction within memory window.
+    Warm,
+    /// Stress at or above threshold — confrontational or withdrawn.
+    Hostile,
+    /// Actively engaged in a scheduled activity — task-focused.
+    Focused,
+}
+
+// ---------------------------------------------------------------------------
+// MoodState component
+// ---------------------------------------------------------------------------
+
+/// Per-NPC mood component — wraps NpcMood for ECS queries.
+///
+/// Updated each tick by `update_mood` for Active-tier NPCs.
+/// Read by: dialogue Layer 4 (via CurrentMood sync), tell system (#337),
+/// monologue tone selection (D-016, future scope).
+#[derive(Component, Debug, Clone, Default, Serialize, Deserialize)]
+pub struct MoodState {
+    pub mood: NpcMood,
+    /// Tick when mood last changed — guards against thrashing in tests.
+    pub changed_tick: u64,
+}
+
+// ---------------------------------------------------------------------------
+// Mood mapping: NpcMood → content::line_pool::Mood
+// ---------------------------------------------------------------------------
+
+/// Map NPC simulation mood to the content dialogue tag.
+///
+/// Bridges the simulation FSM (NpcMood) with the dialogue line pool system
+/// (content::line_pool::Mood). The mapping is intentionally lossy in some
+/// directions — multiple simulation moods map to the same content tag when
+/// the distinction matters for behavior but not for line selection.
+pub fn mood_to_content_mood(mood: NpcMood) -> ContentMood {
+    match mood {
+        NpcMood::Neutral => ContentMood::Comfortable,
+        NpcMood::Anxious => ContentMood::Worried,
+        NpcMood::Frustrated => ContentMood::Conflicted,
+        NpcMood::Content => ContentMood::Relieved,
+        NpcMood::Suspicious => ContentMood::Suspicious,
+        NpcMood::Warm => ContentMood::Fond,
+        NpcMood::Hostile => ContentMood::Concerned,
+        NpcMood::Focused => ContentMood::Focused,
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Mood derivation (pure, testable)
+// ---------------------------------------------------------------------------
+
+/// Stress fraction threshold for Anxious: 60% of tolerance threshold.
+///
+/// Uses integer multiplication to avoid division:
+///   Anxious when `current_stress * 100 >= threshold * ANXIOUS_STRESS_NUMERATOR`
+/// Equivalent to: `current_stress >= threshold * 0.60`
+const ANXIOUS_STRESS_NUMERATOR: i16 = 60;
+
+/// Stress level below which an NPC is considered Content (no notable pressure).
+const CONTENT_STRESS_CEILING: i16 = 20;
+
+/// Minimum stress for Evening → Frustrated (avoids Frustrated at zero stress).
+const FRUSTRATED_STRESS_FLOOR: i16 = 10;
+
+/// Derive NPC mood from simulation inputs.
+///
+/// Priority ordering (high to low):
+///   1. Hostile  — stress at or above threshold
+///   2. Anxious  — stress at 60% of threshold or above
+///   3. Warm     — recent positive player interaction
+///   4. Frustrated — Evening phase with non-trivial stress
+///   5. Content  — very low stress (< CONTENT_STRESS_CEILING)
+///   6. Neutral  — everything else
+///
+/// Inputs are all integer or enum — no floats (D-010 determinism).
+///
+/// `warm_active`: set by InteractionMemory (#325, Sprint 14) when a positive
+/// interaction occurred within the memory window. Placeholder `false` until
+/// #325 is wired.
+pub fn derive_mood(
+    current_stress: i16,
+    threshold: i16,
+    phase: DayPhase,
+    warm_active: bool,
+) -> NpcMood {
+    // 1. Hostile: at or above threshold
+    if current_stress >= threshold {
+        return NpcMood::Hostile;
+    }
+
+    // 2. Anxious: above 60% of threshold.
+    // Guard: skip if threshold == 0 (divide-by-zero equivalent — entity
+    // has no tolerance and is already Hostile from rule 1).
+    if threshold > 0 && current_stress * 100 >= threshold * ANXIOUS_STRESS_NUMERATOR {
+        return NpcMood::Anxious;
+    }
+
+    // 3. Warm: recent positive interaction (priority over Frustrated/Content)
+    if warm_active {
+        return NpcMood::Warm;
+    }
+
+    // 4. Frustrated: Evening phase with non-trivial stress
+    if phase == DayPhase::Evening && current_stress >= FRUSTRATED_STRESS_FLOOR {
+        return NpcMood::Frustrated;
+    }
+
+    // 5. Content: very low stress
+    if current_stress < CONTENT_STRESS_CEILING {
+        return NpcMood::Content;
+    }
+
+    // 6. Neutral: moderate stress, no special conditions
+    NpcMood::Neutral
+}
+
+// ---------------------------------------------------------------------------
+// System: update_mood
+// ---------------------------------------------------------------------------
+
+/// System: update NpcMood and sync CurrentMood for Active-tier NPCs.
+///
+/// Reads `ToleranceThreshold` stress and `SimulationTime` day phase to derive
+/// the new mood. Updates `MoodState` when mood changes (records changed_tick).
+/// Syncs `CurrentMood` (used by dialogue Layer 4) every tick regardless of
+/// whether MoodState changed.
+///
+/// Scoped to `ActiveSim` — Background-tier NPCs retain their last mood state
+/// (D-026). This is intentional: background NPCs simulate passage of time via
+/// last-known state, not per-tick derivation.
+///
+/// TODO(#325): wire `warm_active` from `InteractionMemory` when Sprint 14 #325 lands.
+pub fn update_mood(
+    time: Res<SimulationTime>,
+    mut query: Query<
+        (
+            &mut MoodState,
+            Option<&mut CurrentMood>,
+            Option<&ToleranceThreshold>,
+        ),
+        (With<Npc>, With<ActiveSim>),
+    >,
+) {
+    let phase = time.day_phase();
+    let tick = time.tick;
+
+    for (mut mood_state, current_mood_opt, tolerance_opt) in query.iter_mut() {
+        let (stress, threshold) = tolerance_opt
+            .map(|t| (t.current_stress, t.threshold))
+            .unwrap_or((0, 50)); // Default: no stress, moderate threshold
+
+        // TODO(#325): query InteractionMemory.recent_positive_interaction()
+        let warm_active = false;
+
+        let new_mood = derive_mood(stress, threshold, phase, warm_active);
+
+        if mood_state.mood != new_mood {
+            mood_state.mood = new_mood;
+            mood_state.changed_tick = tick;
+        }
+
+        // Sync CurrentMood for dialogue pipeline — always, not just on change.
+        // CurrentMood drives Layer 4 scoring; it must reflect current simulation
+        // state even if MoodState itself didn't change this tick.
+        if let Some(mut current_mood) = current_mood_opt {
+            current_mood.0 = mood_to_content_mood(new_mood);
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::npc::{Npc, ToleranceThreshold};
+    use crate::simulation::dialogue::CurrentMood;
+    use crate::simulation::tier::{ActiveSim, BackgroundSim};
+    use crate::simulation::time::{DayPhase, SimulationTime};
+    use bevy_ecs::world::World;
+
+    // --- derive_mood unit tests ---
+
+    #[test]
+    fn mood_hostile_when_stress_equals_threshold() {
+        assert_eq!(
+            derive_mood(50, 50, DayPhase::Morning, false),
+            NpcMood::Hostile
+        );
+    }
+
+    #[test]
+    fn mood_hostile_when_stress_above_threshold() {
+        assert_eq!(
+            derive_mood(80, 50, DayPhase::Morning, false),
+            NpcMood::Hostile
+        );
+    }
+
+    #[test]
+    fn mood_anxious_at_60_percent_threshold() {
+        // 60% of threshold=100 is 60. stress=60 → Anxious.
+        assert_eq!(
+            derive_mood(60, 100, DayPhase::Morning, false),
+            NpcMood::Anxious
+        );
+    }
+
+    #[test]
+    fn mood_anxious_boundary_above() {
+        // threshold=50: 60% = 30. stress=30 → Anxious (30*100=3000 >= 50*60=3000).
+        assert_eq!(
+            derive_mood(30, 50, DayPhase::Morning, false),
+            NpcMood::Anxious
+        );
+    }
+
+    #[test]
+    fn mood_not_anxious_just_below_boundary() {
+        // threshold=50: 60% = 30. stress=29 → not Anxious (29*100=2900 < 3000).
+        // stress=29 < 20 is false, so → Neutral.
+        assert_eq!(
+            derive_mood(29, 50, DayPhase::Morning, false),
+            NpcMood::Neutral
+        );
+    }
+
+    #[test]
+    fn mood_warm_when_positive_interaction() {
+        assert_eq!(
+            derive_mood(0, 50, DayPhase::Morning, true),
+            NpcMood::Warm
+        );
+    }
+
+    #[test]
+    fn mood_frustrated_when_evening_with_stress() {
+        // stress=25 (not hostile/anxious), Evening phase → Frustrated
+        assert_eq!(
+            derive_mood(25, 50, DayPhase::Evening, false),
+            NpcMood::Frustrated
+        );
+    }
+
+    #[test]
+    fn mood_not_frustrated_in_morning() {
+        assert_eq!(
+            derive_mood(25, 50, DayPhase::Morning, false),
+            NpcMood::Neutral
+        );
+    }
+
+    #[test]
+    fn mood_not_frustrated_when_stress_below_floor() {
+        // stress=5 < FRUSTRATED_STRESS_FLOOR=10 → Content (stress < 20)
+        assert_eq!(
+            derive_mood(5, 50, DayPhase::Evening, false),
+            NpcMood::Content
+        );
+    }
+
+    #[test]
+    fn mood_content_when_low_stress() {
+        assert_eq!(
+            derive_mood(15, 50, DayPhase::Morning, false),
+            NpcMood::Content
+        );
+    }
+
+    #[test]
+    fn mood_content_boundary_at_19() {
+        // stress=19 < CONTENT_STRESS_CEILING=20 → Content
+        assert_eq!(
+            derive_mood(19, 50, DayPhase::Morning, false),
+            NpcMood::Content
+        );
+    }
+
+    #[test]
+    fn mood_neutral_otherwise() {
+        // stress=25, not anxious (25*100=2500 < 50*60=3000), not Warm, morning, not Content
+        // Wait: 25*100=2500, 50*60=3000 → not Anxious. 25 >= 20 → not Content. Morning → not Frustrated. → Neutral
+        assert_eq!(
+            derive_mood(25, 50, DayPhase::Morning, false),
+            NpcMood::Neutral
+        );
+    }
+
+    #[test]
+    fn mood_priority_hostile_over_anxious_at_threshold() {
+        // At exactly threshold → Hostile, not Anxious
+        assert_eq!(
+            derive_mood(50, 50, DayPhase::Morning, false),
+            NpcMood::Hostile
+        );
+    }
+
+    #[test]
+    fn mood_priority_hostile_over_frustrated_evening() {
+        assert_eq!(
+            derive_mood(50, 50, DayPhase::Evening, false),
+            NpcMood::Hostile
+        );
+    }
+
+    #[test]
+    fn mood_priority_anxious_over_warm() {
+        // Anxious takes priority over Warm interaction
+        assert_eq!(
+            derive_mood(60, 100, DayPhase::Morning, true),
+            NpcMood::Anxious
+        );
+    }
+
+    #[test]
+    fn mood_priority_warm_over_frustrated() {
+        // Warm takes priority over Frustrated (checked before Evening test)
+        assert_eq!(
+            derive_mood(25, 50, DayPhase::Evening, true),
+            NpcMood::Warm
+        );
+    }
+
+    #[test]
+    fn mood_zero_threshold_is_hostile() {
+        // stress=0, threshold=0: 0 >= 0 → Hostile
+        assert_eq!(
+            derive_mood(0, 0, DayPhase::Morning, false),
+            NpcMood::Hostile
+        );
+    }
+
+    #[test]
+    fn mood_content_zero_stress_moderate_threshold() {
+        // stress=0, threshold=50: not hostile, not anxious (threshold > 0, 0*100=0 < 50*60=3000),
+        // not warm, not evening, stress < 20 → Content
+        assert_eq!(
+            derive_mood(0, 50, DayPhase::Morning, false),
+            NpcMood::Content
+        );
+    }
+
+    // --- mood_to_content_mood mapping coverage ---
+
+    #[test]
+    fn mood_mapping_covers_all_variants() {
+        for mood in [
+            NpcMood::Neutral,
+            NpcMood::Anxious,
+            NpcMood::Frustrated,
+            NpcMood::Content,
+            NpcMood::Suspicious,
+            NpcMood::Warm,
+            NpcMood::Hostile,
+            NpcMood::Focused,
+        ] {
+            let _ = mood_to_content_mood(mood); // must not panic
+        }
+    }
+
+    #[test]
+    fn mood_mapping_anxious_is_worried() {
+        assert_eq!(mood_to_content_mood(NpcMood::Anxious), ContentMood::Worried);
+    }
+
+    #[test]
+    fn mood_mapping_warm_is_fond() {
+        assert_eq!(mood_to_content_mood(NpcMood::Warm), ContentMood::Fond);
+    }
+
+    #[test]
+    fn mood_mapping_suspicious_is_suspicious() {
+        assert_eq!(
+            mood_to_content_mood(NpcMood::Suspicious),
+            ContentMood::Suspicious
+        );
+    }
+
+    #[test]
+    fn mood_mapping_focused_is_focused() {
+        assert_eq!(mood_to_content_mood(NpcMood::Focused), ContentMood::Focused);
+    }
+
+    // --- update_mood system integration tests ---
+
+    fn setup_world() -> World {
+        let mut world = World::new();
+        world.init_resource::<SimulationTime>();
+        world
+    }
+
+    #[test]
+    fn update_mood_sets_hostile_when_stress_at_threshold() {
+        let mut world = setup_world();
+
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                CurrentMood::default(),
+                ToleranceThreshold {
+                    current_stress: 50,
+                    threshold: 50,
+                },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        assert_eq!(mood_state.mood, NpcMood::Hostile);
+
+        let current_mood = world.get::<CurrentMood>(npc).unwrap();
+        assert_eq!(current_mood.0, ContentMood::Concerned);
+    }
+
+    #[test]
+    fn update_mood_defaults_to_content_without_tolerance() {
+        let mut world = setup_world();
+
+        // No ToleranceThreshold → defaults (stress=0, threshold=50) → Content
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                CurrentMood::default(),
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        assert_eq!(mood_state.mood, NpcMood::Content);
+    }
+
+    #[test]
+    fn update_mood_records_changed_tick_on_transition() {
+        let mut world = setup_world();
+        world.resource_mut::<SimulationTime>().tick = 42;
+
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                // Start Warm, will transition to Hostile
+                MoodState {
+                    mood: NpcMood::Warm,
+                    changed_tick: 0,
+                },
+                CurrentMood::default(),
+                ToleranceThreshold {
+                    current_stress: 50,
+                    threshold: 50,
+                },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        assert_eq!(mood_state.mood, NpcMood::Hostile);
+        assert_eq!(mood_state.changed_tick, 42);
+    }
+
+    #[test]
+    fn update_mood_does_not_update_changed_tick_when_unchanged() {
+        let mut world = setup_world();
+        world.resource_mut::<SimulationTime>().tick = 42;
+
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                // Already Content; no tolerance → will derive Content again
+                MoodState {
+                    mood: NpcMood::Content,
+                    changed_tick: 5,
+                },
+                CurrentMood::default(),
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        assert_eq!(mood_state.mood, NpcMood::Content);
+        assert_eq!(mood_state.changed_tick, 5); // unchanged
+    }
+
+    #[test]
+    fn update_mood_skips_background_npcs() {
+        let mut world = setup_world();
+
+        // BackgroundSim NPC — must not be updated
+        let npc = world
+            .spawn((
+                Npc,
+                BackgroundSim,
+                MoodState {
+                    mood: NpcMood::Warm,
+                    changed_tick: 0,
+                },
+                CurrentMood::default(),
+                ToleranceThreshold {
+                    current_stress: 50,
+                    threshold: 50, // Would → Hostile if processed
+                },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        // Must remain Warm — not processed because BackgroundSim, not ActiveSim
+        assert_eq!(mood_state.mood, NpcMood::Warm);
+    }
+
+    #[test]
+    fn update_mood_syncs_current_mood_when_present() {
+        let mut world = setup_world();
+
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                CurrentMood::default(), // Starts at Comfortable
+                ToleranceThreshold {
+                    current_stress: 70,
+                    threshold: 100, // → Anxious (70% of 100)
+                },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        let current_mood = world.get::<CurrentMood>(npc).unwrap();
+        // Anxious maps to Worried
+        assert_eq!(current_mood.0, ContentMood::Worried);
+    }
+
+    #[test]
+    fn update_mood_works_without_current_mood() {
+        let mut world = setup_world();
+
+        // NPC without CurrentMood — system must not panic
+        let npc = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                // No CurrentMood
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world); // must not panic
+
+        let mood_state = world.get::<MoodState>(npc).unwrap();
+        assert_eq!(mood_state.mood, NpcMood::Content);
+    }
+
+    #[test]
+    fn update_mood_multiple_npcs_independent() {
+        let mut world = setup_world();
+
+        let calm = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                CurrentMood::default(),
+                ToleranceThreshold {
+                    current_stress: 5,
+                    threshold: 50,
+                },
+            ))
+            .id();
+
+        let stressed = world
+            .spawn((
+                Npc,
+                ActiveSim,
+                MoodState::default(),
+                CurrentMood::default(),
+                ToleranceThreshold {
+                    current_stress: 50,
+                    threshold: 50,
+                },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(update_mood);
+        schedule.run(&mut world);
+
+        assert_eq!(world.get::<MoodState>(calm).unwrap().mood, NpcMood::Content);
+        assert_eq!(
+            world.get::<MoodState>(stressed).unwrap().mood,
+            NpcMood::Hostile
+        );
+    }
+}