diff --git a/test/battle/ability/big_pecks.c b/test/battle/ability/big_pecks.c
new file mode 100644
index 000000000000..0c61dd3ba3a2
--- /dev/null
+++ b/test/battle/ability/big_pecks.c
@@ -0,0 +1,116 @@
+#include "global.h"
+#include "test/battle.h"
+
+SINGLE_BATTLE_TEST("Big Pecks prevents Defense stage reduction from moves")
+{
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_LEER].effect == EFFECT_DEFENSE_DOWN);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(player, MOVE_LEER); }
+    } SCENE {
+        ABILITY_POPUP(opponent, ABILITY_BIG_PECKS);
+        MESSAGE("The opposing Pidgey's Big Pecks prevents Defense loss!");
+    }
+}
+
+SINGLE_BATTLE_TEST("Big Pecks is ignored by Mold Breaker")
+{
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_LEER].effect == EFFECT_DEFENSE_DOWN);
+        PLAYER(SPECIES_PINSIR) { Ability(ABILITY_MOLD_BREAKER); }
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(player, MOVE_LEER); }
+    } SCENE {
+        ABILITY_POPUP(player, ABILITY_MOLD_BREAKER);
+        MESSAGE("Pinsir breaks the mold!");
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_LEER, player);
+        MESSAGE("The opposing Pidgey's Defense fell!");
+        NONE_OF {
+            ABILITY_POPUP(opponent, ABILITY_BIG_PECKS);
+            MESSAGE("The opposing Pidgey's Big Pecks prevents Defense loss!");
+        }
+    }
+}
+
+SINGLE_BATTLE_TEST("Big Pecks doesn't prevent Defense stage reduction from moves used by the user")
+{
+    GIVEN {
+        ASSUME(MoveHasAdditionalEffectSelf(MOVE_SUPERPOWER, MOVE_EFFECT_ATK_DEF_DOWN) == TRUE);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_SUPERPOWER); }
+        TURN {}
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_SUPERPOWER, opponent);
+        MESSAGE("The opposing Pidgey's Attack fell!");
+        MESSAGE("The opposing Pidgey's Defense fell!");
+    } THEN {
+        EXPECT_EQ(opponent->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+    }
+}
+
+SINGLE_BATTLE_TEST("Big Pecks doesn't prevent Topsy-Turvy")
+{
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_HARDEN].effect == EFFECT_DEFENSE_UP);
+        ASSUME(gMovesInfo[MOVE_TOPSY_TURVY].effect == EFFECT_TOPSY_TURVY);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_HARDEN); MOVE(player, MOVE_TOPSY_TURVY); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_HARDEN, opponent);
+        MESSAGE("The opposing Pidgey's Defense rose!");
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_TOPSY_TURVY, player);
+        MESSAGE("All stat changes on the opposing Pidgey were inverted!");
+    } THEN {
+        EXPECT_EQ(opponent->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+    }
+}
+
+SINGLE_BATTLE_TEST("Big Pecks doesn't prevent Spectral Thief from resetting positive Defense stage changes")
+{
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_HARDEN].effect == EFFECT_DEFENSE_UP);
+        ASSUME(MoveHasAdditionalEffect(MOVE_SPECTRAL_THIEF, MOVE_EFFECT_SPECTRAL_THIEF));
+        ASSUME(gMovesInfo[MOVE_SOAK].effect == EFFECT_SOAK);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(opponent, MOVE_CELEBRATE); MOVE(player,MOVE_SOAK); }
+        TURN { MOVE(opponent, MOVE_HARDEN); MOVE(player, MOVE_SPECTRAL_THIEF); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_HARDEN, opponent);
+        MESSAGE("The opposing Pidgey's Defense rose!");
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_SPECTRAL_THIEF, player);
+        MESSAGE("Wobbuffet stole the target's boosted stats!");
+    } THEN {
+        EXPECT_EQ(opponent->statStages[STAT_DEF], DEFAULT_STAT_STAGE);
+    }
+}
+
+SINGLE_BATTLE_TEST("Big Pecks doesn't prevent receiving negative Defense stage changes from Baton Pass")
+{
+    GIVEN {
+        ASSUME(gMovesInfo[MOVE_LEER].effect == EFFECT_DEFENSE_DOWN);
+        ASSUME(gMovesInfo[MOVE_BATON_PASS].effect == EFFECT_BATON_PASS);
+        PLAYER(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_WOBBUFFET);
+        OPPONENT(SPECIES_PIDGEY) { Ability(ABILITY_BIG_PECKS); }
+    } WHEN {
+        TURN { MOVE(player, MOVE_LEER);
+               MOVE(opponent, MOVE_BATON_PASS);
+               SEND_OUT(opponent, 1);
+        }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_LEER, player);
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_BATON_PASS, opponent);
+        MESSAGE("2 sent out Pidgey!");
+    } THEN {
+        EXPECT_EQ(opponent->statStages[STAT_DEF], DEFAULT_STAT_STAGE - 1);
+    }
+}