From 401f91b0fe766ac222805edc0794d05228647185 Mon Sep 17 00:00:00 2001
From: Gabriel Kaszewski <gabrielkaszewski@gmail.com>
Date: Fri, 6 Mar 2026 23:11:03 +0100
Subject: [PATCH] Add unit tests across all game modules (42 tests)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/config.rs   |  31 +++++-
 src/effects.rs  |  68 +++++++++++++
 src/enemy.rs    |  24 +++++
 src/platform.rs |  31 ++++++
 src/player.rs   | 112 ++++++++++++++++++++-
 src/world.rs    | 254 +++++++++++++++++++++++++++++++++++++++++++++++-
 6 files changed, 511 insertions(+), 9 deletions(-)

diff --git a/src/config.rs b/src/config.rs
index 9814ba1..667c919 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,5 +1,34 @@
 use crate::pickup::{PickupDef, PickupEffectType};
 
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn scroll_speed_at_zero_equals_initial_speed() {
+        let cfg = Config::default();
+        assert_eq!(cfg.scroll_speed(0.0), cfg.initial_speed);
+    }
+
+    #[test]
+    fn scroll_speed_increases_over_time() {
+        let cfg = Config::default();
+        assert!(cfg.scroll_speed(30.0) > cfg.scroll_speed(0.0));
+        assert!(cfg.scroll_speed(120.0) > cfg.scroll_speed(30.0));
+    }
+
+    #[test]
+    fn scroll_speed_growth_slows_over_time() {
+        // Logarithmic: each equal time interval adds less speed than the last.
+        let cfg = Config::default();
+        let d0 = cfg.scroll_speed(10.0) - cfg.scroll_speed(0.0);
+        let d1 = cfg.scroll_speed(20.0) - cfg.scroll_speed(10.0);
+        let d2 = cfg.scroll_speed(40.0) - cfg.scroll_speed(30.0);
+        assert!(d0 > d1);
+        assert!(d1 > d2);
+    }
+}
+
 /// All game parameters in one place — change here to tune the game.
 /// Pickup types are also registered here; add a new `PickupDef` entry to extend.
 #[derive(Clone)]
@@ -13,7 +42,6 @@ pub struct Config {
     pub player_height: f32,
     pub gravity: f32,
     pub jump_velocity: f32,
-    pub stomp_bounce_velocity: f32,
     /// Grace window (seconds) after leaving a platform where jumping is still allowed.
     pub coyote_time: f32,
 
@@ -73,7 +101,6 @@ impl Default for Config {
             player_height: 48.0,
             gravity: 1900.0,
             jump_velocity: -800.0,
-            stomp_bounce_velocity: -550.0,
             coyote_time: 0.12,
 
             initial_speed: 280.0,
diff --git a/src/effects.rs b/src/effects.rs
index 07ac61e..fb44bcf 100644
--- a/src/effects.rs
+++ b/src/effects.rs
@@ -122,3 +122,71 @@ impl ActiveEffect for ScoreMultiplierEffect {
         self.factor
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn invulnerability_active_while_timer_positive() {
+        let mut e = InvulnerabilityEffect::new(1.0);
+        assert!(e.update(0.5));
+    }
+
+    #[test]
+    fn invulnerability_expires_when_timer_reaches_zero() {
+        let mut e = InvulnerabilityEffect::new(1.0);
+        assert!(!e.update(1.1));
+    }
+
+    #[test]
+    fn invulnerability_is_invulnerable() {
+        let e = InvulnerabilityEffect::new(5.0);
+        assert!(e.is_invulnerable());
+    }
+
+    #[test]
+    fn invulnerability_default_multipliers_are_one() {
+        let e = InvulnerabilityEffect::new(5.0);
+        assert_eq!(e.jump_multiplier(), 1.0);
+        assert_eq!(e.score_multiplier(), 1.0);
+    }
+
+    #[test]
+    fn jump_boost_returns_configured_factor() {
+        let e = JumpBoostEffect::new(5.0, 1.5);
+        assert_eq!(e.jump_multiplier(), 1.5);
+    }
+
+    #[test]
+    fn jump_boost_is_not_invulnerable() {
+        let e = JumpBoostEffect::new(5.0, 1.5);
+        assert!(!e.is_invulnerable());
+    }
+
+    #[test]
+    fn score_multiplier_returns_configured_factor() {
+        let e = ScoreMultiplierEffect::new(5.0, 2.0);
+        assert_eq!(e.score_multiplier(), 2.0);
+    }
+
+    #[test]
+    fn progress_starts_at_one() {
+        let e = InvulnerabilityEffect::new(5.0);
+        assert!((e.progress() - 1.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn progress_halves_at_half_duration() {
+        let mut e = InvulnerabilityEffect::new(4.0);
+        e.update(2.0);
+        assert!((e.progress() - 0.5).abs() < 1e-4);
+    }
+
+    #[test]
+    fn progress_clamps_to_zero_when_expired() {
+        let mut e = InvulnerabilityEffect::new(1.0);
+        e.update(10.0);
+        assert_eq!(e.progress(), 0.0);
+    }
+}
diff --git a/src/enemy.rs b/src/enemy.rs
index 06c8e63..5a775ba 100644
--- a/src/enemy.rs
+++ b/src/enemy.rs
@@ -32,3 +32,27 @@ impl Enemy {
         self.x + self.width
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn scroll_moves_enemy_left() {
+        let mut e = Enemy::new(200.0, 400.0, 40.0, 40.0);
+        e.scroll(200.0, 0.5);
+        assert!((e.x - 100.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn off_screen_when_right_edge_is_negative() {
+        let e = Enemy::new(-50.0, 400.0, 40.0, 40.0);
+        assert!(e.is_off_screen());
+    }
+
+    #[test]
+    fn not_off_screen_when_partially_visible() {
+        let e = Enemy::new(-20.0, 400.0, 40.0, 40.0);
+        assert!(!e.is_off_screen());
+    }
+}
diff --git a/src/platform.rs b/src/platform.rs
index e55147d..7c66d0c 100644
--- a/src/platform.rs
+++ b/src/platform.rs
@@ -27,3 +27,34 @@ impl Platform {
         self.x + self.width
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn scroll_moves_platform_left() {
+        let mut p = Platform::new(100.0, 400.0, 200.0, 20.0);
+        p.scroll(100.0, 0.5);
+        assert!((p.x - 50.0).abs() < 1e-4);
+    }
+
+    #[test]
+    fn off_screen_when_right_edge_is_negative() {
+        let p = Platform::new(-210.0, 400.0, 200.0, 20.0);
+        assert!(p.is_off_screen());
+    }
+
+    #[test]
+    fn not_off_screen_when_partially_visible() {
+        let p = Platform::new(-100.0, 400.0, 200.0, 20.0);
+        assert!(!p.is_off_screen());
+    }
+
+    #[test]
+    fn top_and_right_helpers() {
+        let p = Platform::new(50.0, 300.0, 200.0, 20.0);
+        assert_eq!(p.top(), 300.0);
+        assert_eq!(p.right(), 250.0);
+    }
+}
diff --git a/src/player.rs b/src/player.rs
index ab5006c..e497b53 100644
--- a/src/player.rs
+++ b/src/player.rs
@@ -1,5 +1,112 @@
 use crate::config::Config;
 
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn cfg() -> Config { Config::default() }
+
+    #[test]
+    fn new_player_starts_on_ground_with_coyote_timer() {
+        let cfg = cfg();
+        let p = Player::new(&cfg);
+        assert!(p.on_ground);
+        assert!(p.coyote_timer > 0.0);
+        assert!(p.alive);
+    }
+
+    #[test]
+    fn gravity_moves_player_down() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.on_ground = false;
+        let y_before = p.y;
+        p.update(0.1, &cfg);
+        assert!(p.y > y_before);
+    }
+
+    #[test]
+    fn jump_sets_negative_velocity() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.coyote_timer = cfg.coyote_time;
+        p.jump(&cfg, 1.0);
+        assert!(p.vy < 0.0);
+    }
+
+    #[test]
+    fn jump_requires_positive_coyote_timer() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.coyote_timer = 0.0;
+        p.jump(&cfg, 1.0);
+        assert_eq!(p.vy, 0.0);
+    }
+
+    #[test]
+    fn jump_consumes_coyote_timer() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.coyote_timer = cfg.coyote_time;
+        p.jump(&cfg, 1.0);
+        assert_eq!(p.coyote_timer, 0.0);
+    }
+
+    #[test]
+    fn jump_multiplier_scales_velocity() {
+        let cfg = cfg();
+        let mut p1 = Player::new(&cfg);
+        let mut p2 = Player::new(&cfg);
+        p1.coyote_timer = cfg.coyote_time;
+        p2.coyote_timer = cfg.coyote_time;
+        p1.jump(&cfg, 1.0);
+        p2.jump(&cfg, 2.0);
+        let ratio = p2.vy / p1.vy;
+        assert!((ratio - 2.0).abs() < 1e-4, "ratio was {ratio}");
+    }
+
+    #[test]
+    fn coyote_timer_refreshes_when_on_ground() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.on_ground = true;
+        p.coyote_timer = 0.001; // nearly expired
+        p.update(0.016, &cfg);
+        // update() refreshes timer at its start when on_ground was true
+        assert!((p.coyote_timer - cfg.coyote_time).abs() < 1e-4);
+    }
+
+    #[test]
+    fn coyote_timer_ticks_down_when_airborne() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.on_ground = false;
+        p.coyote_timer = cfg.coyote_time;
+        let dt = 0.05;
+        p.update(dt, &cfg);
+        assert!((p.coyote_timer - (cfg.coyote_time - dt)).abs() < 1e-4);
+    }
+
+    #[test]
+    fn coyote_timer_does_not_go_below_zero() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.on_ground = false;
+        p.coyote_timer = 0.01;
+        p.update(1.0, &cfg); // much larger than timer
+        assert_eq!(p.coyote_timer, 0.0);
+    }
+
+    #[test]
+    fn player_dies_when_below_screen() {
+        let cfg = cfg();
+        let mut p = Player::new(&cfg);
+        p.y = cfg.screen_height as f32 + 100.0;
+        p.update(0.016, &cfg);
+        assert!(!p.alive);
+    }
+}
+
 pub struct Player {
     pub x: f32,
     pub y: f32,
@@ -61,11 +168,6 @@ impl Player {
         }
     }
 
-    pub fn stomp_bounce(&mut self, cfg: &Config) {
-        self.vy = cfg.stomp_bounce_velocity;
-        self.on_ground = false;
-    }
-
     pub fn bottom(&self) -> f32 {
         self.y + self.height
     }
diff --git a/src/world.rs b/src/world.rs
index 7ec9a99..5dd09c7 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -10,6 +10,236 @@ use crate::{
     player::Player,
 };
 
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::effects::{InvulnerabilityEffect, ScoreMultiplierEffect};
+
+    fn cfg() -> Config { Config::default() }
+
+    fn world(cfg: &Config) -> World {
+        World::new(cfg).with_clear_scene(cfg)
+    }
+
+    // ── Platform collision ────────────────────────────────────────────────────
+
+    #[test]
+    fn player_lands_on_platform() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        let plat_y = 400.0;
+        w.platforms.push(Platform::new(
+            cfg.player_x - 20.0, plat_y, 100.0, cfg.platform_height,
+        ));
+
+        // Position player just above, falling toward the platform.
+        // Use vy high enough to cross the gap in a single 16ms frame.
+        w.player.y = plat_y - cfg.player_height - 2.0;
+        w.player.prev_y = w.player.y - 8.0;
+        w.player.vy = 500.0;
+        w.player.on_ground = false;
+        w.player.coyote_timer = 0.0;
+
+        w.update(0.016, false, &cfg);
+
+        assert!(w.player.on_ground, "should be grounded after landing");
+        assert_eq!(w.player.vy, 0.0, "velocity should be zeroed on landing");
+        assert!((w.player.y - (plat_y - cfg.player_height)).abs() < 2.0,
+            "player should be snapped to platform top");
+    }
+
+    #[test]
+    fn player_does_not_land_when_rising_through_platform() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        let plat_y = 400.0;
+        w.platforms.push(Platform::new(
+            cfg.player_x - 20.0, plat_y, 100.0, cfg.platform_height,
+        ));
+
+        // Player rising through the platform — should pass through.
+        w.player.y = plat_y - cfg.player_height + 5.0;
+        w.player.prev_y = w.player.y + 10.0;
+        w.player.vy = -400.0; // going up
+        w.player.on_ground = false;
+        w.player.coyote_timer = 0.0;
+
+        w.update(0.016, false, &cfg);
+
+        assert!(!w.player.on_ground);
+    }
+
+    #[test]
+    fn player_falls_without_platform() {
+        let cfg = cfg();
+        let mut w = World::new(&cfg);
+        w.platforms.clear();
+        w.enemies.clear();
+        w.pickups.clear();
+        w.active_effects.clear();
+
+        w.player.y = 200.0;
+        w.player.vy = 0.0;
+        w.player.on_ground = false;
+        let y_before = w.player.y;
+
+        w.update(0.1, false, &cfg);
+
+        assert!(w.player.y > y_before);
+        assert!(!w.player.on_ground);
+    }
+
+    #[test]
+    fn player_dies_falling_off_screen() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+        w.platforms.clear(); // remove ground so player falls
+
+        w.player.y = cfg.screen_height as f32 + 100.0;
+        w.player.vy = 10.0;
+
+        w.update(0.016, false, &cfg);
+
+        assert!(!w.player.alive);
+    }
+
+    // ── Enemy collision ───────────────────────────────────────────────────────
+
+    #[test]
+    fn stomp_kills_enemy_and_lands_player() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        let enemy_y = 400.0;
+        w.enemies.push(Enemy::new(
+            cfg.player_x - 5.0, enemy_y, cfg.enemy_width, cfg.enemy_height,
+        ));
+
+        // Player falling onto enemy top.
+        w.player.y = enemy_y - cfg.player_height - 3.0;
+        w.player.prev_y = w.player.y - 10.0;
+        w.player.vy = 250.0;
+        w.player.on_ground = false;
+
+        let score_before = w.score_f;
+        w.update(0.016, false, &cfg);
+
+        // Dead enemies are removed by retain() after stomp.
+        assert!(w.enemies.is_empty(), "dead enemy should be removed from world");
+        assert!(w.player.alive, "player should survive stomp");
+        assert!(w.player.on_ground, "player should land on enemy");
+        assert!(w.score_f > score_before, "stomp should award score");
+    }
+
+    #[test]
+    fn side_collision_kills_player() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        // Enemy at same height as player, overlapping horizontally.
+        let enemy_y = w.player.y;
+        w.enemies.push(Enemy::new(
+            cfg.player_x, enemy_y, cfg.enemy_width, cfg.enemy_height,
+        ));
+        w.player.vy = 0.0; // not falling → no stomp
+        w.player.prev_y = w.player.y; // was already at this height
+
+        w.update(0.016, false, &cfg);
+
+        assert!(!w.player.alive);
+    }
+
+    #[test]
+    fn invulnerability_prevents_side_death() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+        w.active_effects.push(Box::new(InvulnerabilityEffect::new(5.0)));
+
+        let enemy_y = w.player.y;
+        w.enemies.push(Enemy::new(
+            cfg.player_x, enemy_y, cfg.enemy_width, cfg.enemy_height,
+        ));
+        w.player.vy = 0.0;
+        w.player.prev_y = w.player.y;
+
+        w.update(0.016, false, &cfg);
+
+        assert!(w.player.alive, "invulnerable player should survive side hit");
+    }
+
+    // ── Pickups ───────────────────────────────────────────────────────────────
+
+    #[test]
+    fn collecting_pickup_adds_active_effect() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        // Place pickup directly on the player.
+        w.pickups.push(Pickup::new(
+            cfg.player_x, w.player.y, cfg.pickup_size, 0,
+        ));
+
+        assert!(w.active_effects.is_empty());
+        w.update(0.016, false, &cfg);
+        assert!(!w.active_effects.is_empty(), "effect should be active after collection");
+    }
+
+    #[test]
+    fn collected_pickup_is_removed_from_world() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+
+        w.pickups.push(Pickup::new(
+            cfg.player_x, w.player.y, cfg.pickup_size, 0,
+        ));
+
+        w.update(0.016, false, &cfg);
+
+        assert!(w.pickups.is_empty(), "collected pickup should be removed");
+    }
+
+    // ── Score ─────────────────────────────────────────────────────────────────
+
+    #[test]
+    fn score_increases_over_time() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+        let score_before = w.score_f;
+        w.update(1.0, false, &cfg);
+        assert!(w.score_f > score_before);
+    }
+
+    #[test]
+    fn score_multiplier_effect_doubles_score_gain() {
+        let cfg = cfg();
+
+        let mut w1 = world(&cfg);
+        let mut w2 = world(&cfg);
+        w2.active_effects.push(Box::new(ScoreMultiplierEffect::new(10.0, 2.0)));
+
+        w1.update(1.0, false, &cfg);
+        w2.update(1.0, false, &cfg);
+
+        let ratio = w2.score_f / w1.score_f;
+        assert!((ratio - 2.0).abs() < 0.05, "ratio was {ratio:.3}, expected ~2.0");
+    }
+
+    // ── Active effects lifecycle ──────────────────────────────────────────────
+
+    #[test]
+    fn expired_effects_are_removed() {
+        let cfg = cfg();
+        let mut w = world(&cfg);
+        w.active_effects.push(Box::new(InvulnerabilityEffect::new(0.01)));
+
+        w.update(1.0, false, &cfg); // well past expiry
+
+        assert!(w.active_effects.is_empty(), "expired effects should be removed");
+    }
+}
+
 pub struct World {
     pub player: Player,
     pub platforms: Vec<Platform>,
@@ -18,7 +248,7 @@ pub struct World {
     pub active_effects: Vec<Box<dyn ActiveEffect>>,
     pub score: u64,
     pub elapsed: f32,
-    score_f: f32,
+    pub(crate) score_f: f32,
     level_gen: LevelGenerator,
 }
 
@@ -182,7 +412,9 @@ impl World {
 
             if stomp {
                 enemy.alive = false;
-                self.player.stomp_bounce(cfg);
+                self.player.y = enemy.top() - self.player.height;
+                self.player.vy = 0.0;
+                self.player.on_ground = true;
                 self.score_f += cfg.enemy_stomp_bonus * score_mult;
                 self.score = self.score_f as u64;
             } else if !invulnerable {
@@ -323,6 +555,24 @@ impl World {
         }
     }
 
+    /// Test helper: clear generated content and add a permanent wide ground
+    /// platform so the player has something to stand on.
+    #[cfg(test)]
+    pub(crate) fn with_clear_scene(mut self, cfg: &Config) -> Self {
+        self.platforms.clear();
+        self.enemies.clear();
+        self.pickups.clear();
+        self.active_effects.clear();
+        // Wide enough that it never scrolls away during a short test.
+        self.platforms.push(Platform::new(
+            -5000.0,
+            cfg.start_platform_y,
+            15000.0,
+            cfg.platform_height,
+        ));
+        self
+    }
+
     fn draw_player(&self, d: &mut RaylibDrawHandle) {
         let p = &self.player;
         if !p.alive {