test: add tests for terrain shaping parameters

tests/testTerrain.cpp

@@ -0,0 +1,90 @@
+#include "testHarness.h"
+#include "vf/Terrain.h"
+
+using namespace vf;
+
+namespace {
+
+int topSolid(const World& world, int gx, int gz, int worldHeight) {
+    for (int y = worldHeight - 1; y >= 0; --y)
+        if (world.solidAt(gx, y, gz)) return y;
+    return -1;
+}
+
+} // namespace
+
+VF_TEST(terrainIsDeterministicForSeed) {
+    TerrainParams params;
+    params.chunksX = 2;
+    params.chunksZ = 2;
+    params.worldHeight = 48;
+    World a, b;
+    generateTerrain(a, params);
+    generateTerrain(b, params);
+
+    for (int x = 0; x < 2 * chunkSize; ++x)
+        for (int y = 0; y < params.worldHeight; ++y)
+            for (int z = 0; z < 2 * chunkSize; ++z)
+                CHECK(a.blockAt(x, y, z) == b.blockAt(x, y, z));
+}
+
+VF_TEST(terrainDiffersBetweenSeeds) {
+    TerrainParams p1;
+    p1.chunksX = 2;
+    p1.chunksZ = 2;
+    p1.worldHeight = 48;
+    TerrainParams p2 = p1;
+    p2.seed = 9001u;
+
+    World a, b;
+    generateTerrain(a, p1);
+    generateTerrain(b, p2);
+
+    bool anyDifference = false;
+    for (int x = 0; x < 2 * chunkSize && !anyDifference; ++x)
+        for (int z = 0; z < 2 * chunkSize && !anyDifference; ++z)
+            if (topSolid(a, x, z, p1.worldHeight) != topSolid(b, x, z, p2.worldHeight))
+                anyDifference = true;
+    CHECK(anyDifference);
+}
+
+VF_TEST(terrainHeightMatchesColumnHelperAndIsBounded) {
+    TerrainParams params;
+    params.chunksX = 2;
+    params.chunksZ = 2;
+    params.worldHeight = 48;
+    World world;
+    generateTerrain(world, params);
+
+    int minH = params.worldHeight;
+    int maxH = 0;
+    for (int x = 0; x < 2 * chunkSize; ++x) {
+        for (int z = 0; z < 2 * chunkSize; ++z) {
+            int top = topSolid(world, x, z, params.worldHeight);
+            int expected = columnHeight(params.seed, params, x, z);
+            CHECK_EQ(top, expected);
+            CHECK(top >= 1 && top < params.worldHeight);
+            if (top < minH) minH = top;
+            if (top > maxH) maxH = top;
+        }
+    }
+    CHECK(minH < maxH);   // terrain is not flat
+}
+
+VF_TEST(terrainColumnAboveSurfaceIsNotStoneCore) {
+    TerrainParams params;
+    params.chunksX = 1;
+    params.chunksZ = 1;
+    params.worldHeight = 48;
+    World world;
+    generateTerrain(world, params);
+
+    for (int x = 0; x < chunkSize; ++x) {
+        for (int z = 0; z < chunkSize; ++z) {
+            int top = topSolid(world, x, z, params.worldHeight);
+            Block below = world.blockAt(x, 0, z);
+            CHECK(below == Block::Stone);   // bedrock-ish base is always stone
+            CHECK(world.solidAt(x, top, z));
+        }
+    }
+}