diff --git a/tests/testNetherGen.cpp b/tests/testNetherGen.cpp
new file mode 100644
index 0000000..f52b285
--- /dev/null
+++ b/tests/testNetherGen.cpp
@@ -0,0 +1,166 @@
+#include "testHarness.h"
+#include "vf/NetherGen.h"
+
+#include <map>
+#include <set>
+
+using namespace vf;
+
+namespace {
+
+std::map<Block, int> censusColumn(const World& world, int columnX, int columnZ, int ceilingY) {
+    std::map<Block, int> tally;
+    int ox = columnX * chunkSize;
+    int oz = columnZ * chunkSize;
+    for (int gx = ox; gx < ox + chunkSize; ++gx)
+        for (int gz = oz; gz < oz + chunkSize; ++gz)
+            for (int gy = 0; gy < ceilingY; ++gy)
+                ++tally[world.blockAt(gx, gy, gz)];
+    return tally;
+}
+
+int countOf(const std::map<Block, int>& tally, Block block) {
+    auto it = tally.find(block);
+    return it == tally.end() ? 0 : it->second;
+}
+
+int findColumnWithBiome(const NetherGenerator& generator, NetherBiome biome, int& outColumnX,
+                        int& outColumnZ) {
+    for (int columnX = -40; columnX <= 40; ++columnX) {
+        for (int columnZ = -40; columnZ <= 40; ++columnZ) {
+            int probeX = columnX * chunkSize + 8;
+            int probeZ = columnZ * chunkSize + 8;
+            if (generator.biomeAt(probeX, probeZ) != biome) continue;
+            outColumnX = columnX;
+            outColumnZ = columnZ;
+            return 1;
+        }
+    }
+    return 0;
+}
+
+} // namespace
+
+VF_TEST(netherChunkGenerationRepeatsExactlyOnTheSameSeed) {
+    NetherGenerator generator;
+    Chunk first, second;
+    generator.generateChunk(first, {2, 3, -4});
+    generator.generateChunk(second, {2, 3, -4});
+    CHECK(first.raw() == second.raw());
+
+    Chunk elsewhere;
+    generator.generateChunk(elsewhere, {2, 3, 5});
+    CHECK(first.raw() != elsewhere.raw());
+
+    NetherGenerator::Params other;
+    other.seed = 9001u;
+    NetherGenerator reseeded(other);
+
+    World original, alternative;
+    generator.generateColumn(original, 2, -4);
+    reseeded.generateColumn(alternative, 2, -4);
+
+    int differingChunks = 0;
+    for (const auto& entry : original.allChunks()) {
+        const Chunk* twin = alternative.chunkAt(entry.first);
+        if (!twin || twin->raw() != entry.second->raw()) ++differingChunks;
+    }
+    CHECK(differingChunks > 0);
+}
+
+VF_TEST(netherColumnIsByteIdenticalAcrossTwoRuns) {
+    NetherGenerator generator;
+    World first, second;
+    generator.generateColumn(first, -3, 6);
+    generator.generateColumn(second, -3, 6);
+
+    CHECK_EQ(first.chunkCount(), second.chunkCount());
+    CHECK_EQ(first.chunkCount(), static_cast<std::size_t>(generator.stackChunkCount()));
+
+    int mismatches = 0;
+    for (const auto& entry : first.allChunks()) {
+        const Chunk* twin = second.chunkAt(entry.first);
+        if (!twin || twin->raw() != entry.second->raw()) ++mismatches;
+    }
+    CHECK_EQ(mismatches, 0);
+}
+
+VF_TEST(netherGenerationStaysInsideTheColumnItWasAskedFor) {
+    NetherGenerator generator;
+    World world;
+    generator.generateColumn(world, 5, 7);
+
+    int strays = 0;
+    for (const auto& entry : world.allChunks())
+        if (entry.first.x != 5 || entry.first.z != 7) ++strays;
+    CHECK_EQ(strays, 0);
+}
+
+VF_TEST(netherIsSealedByBedrockAtTheFloorAndTheRoof) {
+    NetherGenerator generator;
+    const NetherGenerator::Params& params = generator.settings();
+    World world;
+    generator.generateColumn(world, 0, 0);
+
+    int floorGaps = 0;
+    int roofGaps = 0;
+    for (int gx = 0; gx < chunkSize; ++gx) {
+        for (int gz = 0; gz < chunkSize; ++gz) {
+            if (world.blockAt(gx, params.floorY, gz) != Block::Bedrock) ++floorGaps;
+            if (world.blockAt(gx, params.ceilingY - 1, gz) != Block::Bedrock) ++roofGaps;
+        }
+    }
+    CHECK_EQ(floorGaps, 0);
+    CHECK_EQ(roofGaps, 0);
+
+    // The bands just inside those layers are ragged, not uniformly bedrock.
+    int raggedFloor = 0;
+    for (int gx = 0; gx < chunkSize; ++gx)
+        for (int gz = 0; gz < chunkSize; ++gz)
+            if (generator.isBedrock(gx, params.floorY + 2, gz)) ++raggedFloor;
+    CHECK(raggedFloor > 0);
+    CHECK(raggedFloor < chunkSize * chunkSize);
+    CHECK(!generator.isBedrock(0, 60, 0));
+}
+
+VF_TEST(netherCavernSitsBetweenTheFloorAndTheRoofMass) {
+    NetherGenerator generator;
+    const NetherGenerator::Params& params = generator.settings();
+
+    int drownedColumns = 0;
+    int dryColumns = 0;
+    for (int gx = -400; gx <= 400; gx += 37) {
+        for (int gz = -400; gz <= 400; gz += 37) {
+            NetherColumn column = generator.columnAt(gx, gz);
+            CHECK(column.floorHeight > params.floorY);
+            CHECK(column.ceilingHeight < params.ceilingY - 1);
+            CHECK(column.cavernHeight() >= 9);
+            CHECK_EQ(column.lavaLevel, params.lavaLevel);
+            if (column.drowned) ++drownedColumns;
+            else ++dryColumns;
+        }
+    }
+    CHECK(drownedColumns > 0);
+    CHECK(dryColumns > 0);
+}
+
+VF_TEST(netherLavaSeaLeavesNoAirBelowItsSurface) {
+    NetherGenerator generator;
+    const NetherGenerator::Params& params = generator.settings();
+
+    int airBelowLava = 0;
+    int lavaSamples = 0;
+    for (int gx = -120; gx <= 120; gx += 11) {
+        for (int gz = -120; gz <= 120; gz += 11) {
+            NetherColumn column = generator.columnAt(gx, gz);
+            for (int gy = params.floorY + 1; gy <= params.lavaLevel; ++gy) {
+                Block block = generator.blockAt(column, gx, gy, gz);
+                if (block == Block::Air) ++airBelowLava;
+                if (block == Block::Lava) ++lavaSamples;
+            }
+        }
+    }
+    CHECK_EQ(airBelowLava, 0);
+    CHECK(lavaSamples > 0);
+}
+