diff --git a/tests/testSpawning.cpp b/tests/testSpawning.cpp
index bb4bc1c..d976463 100644
--- a/tests/testSpawning.cpp
+++ b/tests/testSpawning.cpp
@@ -156,3 +156,161 @@ VF_TEST(aNocturnalRuleIsRefusedInBroadDaylight) {
           SpawnDenial::WrongTimeOfDay);
 }
 
+VF_TEST(theWrongBlockUnderfootIsRefused) {
+    World world = plateWorld(Block::Grass);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    SpawnRule rule = zombieRule();
+    rule.groundBlocks = {Block::Sand};
+    CHECK(checkSpawnRule(rule, env, originCell(), MobCap{}) == SpawnDenial::UnsuitableGround);
+
+    rule.groundBlocks = {Block::Sand, Block::Grass};
+    CHECK(checkSpawnRule(rule, env, originCell(), MobCap{}) == SpawnDenial::None);
+}
+
+VF_TEST(aCeilingPressedOntoTheSpawnCellIsRefusedForNoHeadroom) {
+    World world = plateWorld(Block::Grass);
+    world.setBlock(0, spawnY + 1, 0, Block::Stone);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    CHECK(checkSpawnRule(zombieRule(), env, originCell(), MobCap{}) == SpawnDenial::NoHeadroom);
+
+    SpawnRule crawler = zombieRule();
+    crawler.requiredHeadroom = 1;
+    CHECK(checkSpawnRule(crawler, env, originCell(), MobCap{}) == SpawnDenial::None);
+}
+
+VF_TEST(aTorchLitCellIsRefusedForTooMuchBlockLight) {
+    World world = plateWorld(Block::Grass);
+    world.setBlock(1, spawnY, 1, Block::Glowstone);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    CHECK(env.blockLightAt(originCell()) > zombieRule().maxBlockLight);
+    CHECK(checkSpawnRule(zombieRule(), env, originCell(), MobCap{}) ==
+          SpawnDenial::BlockLightTooHigh);
+
+    // The same cell far from the emitter is dark enough again.
+    Vec3i faraway{30, spawnY, 30};
+    CHECK_EQ(env.blockLightAt(faraway), 0);
+    CHECK(checkSpawnRule(zombieRule(), env, faraway, MobCap{}) == SpawnDenial::None);
+}
+
+VF_TEST(anOpenSkyAtNoonIsRefusedForTooMuchSkyLight) {
+    World world = plateWorld(Block::Grass);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+    env.daytime = true;
+
+    SpawnRule daywalker = zombieRule();
+    daywalker.dayAllowed = true;
+    CHECK_EQ(env.skyLightAt(originCell()), 15);
+    CHECK(checkSpawnRule(daywalker, env, originCell(), MobCap{}) ==
+          SpawnDenial::SkyLightTooHigh);
+}
+
+VF_TEST(aSunlessCellIsRefusedForTooLittleLight) {
+    World world = plateWorld(Block::Grass);
+    for (int x = -fieldSpan; x <= fieldSpan; ++x) {
+        for (int z = -fieldSpan; z <= fieldSpan; ++z) world.setBlock(x, floorY + 4, z, Block::Stone);
+    }
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+    env.daytime = true;
+    env.playerPosition = {20.5f, static_cast<float>(spawnY), 0.5f};
+
+    CHECK_EQ(env.skyLightAt(originCell()), 0);
+    CHECK(checkSpawnRule(sheepRule(), env, originCell(), MobCap{}) == SpawnDenial::LightTooLow);
+}
+
+VF_TEST(theSpawnRingAroundThePlayerIsRefusedOnBothSides) {
+    World world = plateWorld(Block::Grass);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    env.playerPosition = {0.5f, static_cast<float>(spawnY), 0.5f};
+    CHECK(checkSpawnRule(zombieRule(), env, originCell(), MobCap{}) ==
+          SpawnDenial::TooCloseToPlayer);
+
+    env.playerPosition = {400.5f, static_cast<float>(spawnY), 0.5f};
+    CHECK(checkSpawnRule(zombieRule(), env, originCell(), MobCap{}) ==
+          SpawnDenial::TooFarFromPlayer);
+}
+
+VF_TEST(aColumnWithNoFloorReportsThatNoCellWasStandable) {
+    World world;
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    Vec3i cell;
+    CHECK(!pickSpawnCell(env, Vec3i{0, 0, 0}, 99u, 0, cell));
+
+    Spawner spawner;
+    SpawnResult result = spawner.runColumn(env, SpawnCategory::Hostile, Vec3i{0, 0, 0}, 99u, 0);
+    CHECK(result.denial == SpawnDenial::NoStandableCell);
+    CHECK(!result.spawned);
+    CHECK_EQ(spawner.denialCount(SpawnDenial::NoStandableCell), 1);
+}
+
+VF_TEST(aCategoryWithNoRulesReportsThatNoRuleMatched) {
+    World world = plateWorld(Block::Grass);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+
+    Spawner spawner;
+    SpawnResult result = spawner.runColumn(env, SpawnCategory::Water, Vec3i{0, 0, 0}, 7u, 0);
+    CHECK(result.denial == SpawnDenial::NoRuleMatched);
+    CHECK_EQ(spawner.denialCount(SpawnDenial::NoRuleMatched), 1);
+
+    // Adding one water rule is all it takes for the category to come alive.
+    std::vector<SpawnRule> rules = defaultSpawnRules();
+    SpawnRule diver = sheepRule();
+    diver.category = SpawnCategory::Water;
+    rules.push_back(diver);
+    Spawner wet(rules);
+    CHECK(wet.pickRule(env, SpawnCategory::Water, 3u) != nullptr);
+}
+
+VF_TEST(theMobCapGrowsWithTheNumberOfLoadedChunks) {
+    MobCap cap;
+    CHECK_EQ(cap.capFor(SpawnCategory::Hostile, 289), cap.baseCapFor(SpawnCategory::Hostile));
+    CHECK_EQ(cap.capFor(SpawnCategory::Hostile, 578), cap.baseCapFor(SpawnCategory::Hostile) * 2);
+    CHECK_EQ(cap.capFor(SpawnCategory::Hostile, 0), 0);
+
+    int previous = -1;
+    for (int chunks = 0; chunks <= 1156; chunks += 17) {
+        int current = cap.capFor(SpawnCategory::Hostile, chunks);
+        CHECK(current >= previous);
+        previous = current;
+    }
+    CHECK(cap.capFor(SpawnCategory::Hostile, 1156) > cap.capFor(SpawnCategory::Hostile, 289));
+    CHECK(cap.capFor(SpawnCategory::Passive, 289) < cap.capFor(SpawnCategory::Hostile, 289));
+
+    // A quarter of the world loaded holds roughly a quarter of the mobs.
+    CHECK_EQ(cap.capFor(SpawnCategory::Hostile, 72), 17);
+}
+
+VF_TEST(aRunningCycleStopsSpawningOnceTheCapIsReached) {
+    World world = plateWorld(Block::Grass);
+    LightField light = bakeLight(world);
+    SpawnEnvironment env = nightEnvironment(world, light);
+    env.loadedChunks = 17;
+    env.playerPosition = {0.5f, static_cast<float>(spawnY), 0.5f};
+
+    MobCap cap;
+    int limit = cap.capFor(SpawnCategory::Hostile, env.loadedChunks);
+    CHECK(limit > 0);
+
+    std::vector<Vec3i> columns;
+    for (int cx = -2; cx <= 2; ++cx) {
+        for (int cz = -2; cz <= 2; ++cz) columns.push_back(Vec3i{cx, 0, cz});
+    }
+
+    Spawner spawner;
+    spawner.setAttemptsPerColumn(6);
+    for (int cycle = 0; cycle < 12; ++cycle) {
+        spawner.runCycle(env, SpawnCategory::Hostile, columns, 1234u + static_cast<uint64_t>(cycle));
+    }
+