test:

- Added biome shared child style test, expected to fail until the fix

Ref.: https://github.com/VolmitSoftware/Iris/issues/1251

core/src/test/java/art/arcane/iris/generation/biome/IrisBiomeChildrenGeneratorTest.java

@@ -0,0 +1,67 @@
+package art.arcane.iris.generation.biome;
+
+import art.arcane.iris.generation.noise.IrisGeneratorStyle;
+import art.arcane.iris.generation.noise.NoiseStyle;
+import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.testsupport.ExpectedToFailUntilFixed;
+import art.arcane.iris.testsupport.ExpectedToFailUntilFixedRule;
+import art.arcane.iris.testsupport.RunningEnginePackData;
+import art.arcane.volmlib.util.math.RNG;
+import org.junit.Rule;
+import org.junit.Test;
+
+import static art.arcane.iris.testsupport.GeneratorSampling.sampleAtBlocks;
+import static org.junit.Assert.assertArrayEquals;
+
+public class IrisBiomeChildrenGeneratorTest {
+    private static final String SHARED_CHILD_STYLE_GENERATOR_BUG =
+            "IrisBiome scales the shared child style generator instead of its own. "
+                    + "Ref.: https://github.com/VolmitSoftware/Iris/issues/1251";
+    private static final long WORLD_SEED = 7L;
+    private static final int CHILDREN_SIGNATURE = 123;
+    private static final double CHILD_SHRINK_FACTOR = 4D;
+    private static final double[][] SAMPLE_BLOCKS = {{1000D, -2000D}, {12.5D, -7.25D}, {-517D, 333D}};
+
+    private final IrisData packData = RunningEnginePackData.create();
+    private final IrisBiome biome = createBiomeWithSimplexChildStyle(packData);
+
+    @Rule
+    public final ExpectedToFailUntilFixedRule expectedFailures = new ExpectedToFailUntilFixedRule();
+
+    @ExpectedToFailUntilFixed(SHARED_CHILD_STYLE_GENERATOR_BUG)
+    @Test
+    public void doesBuildingTheChildrenGeneratorLeaveTheSharedChildStyleGeneratorUnscaled() {
+        assertArrayEquals(sampleUntouchedSharedChildStyleGenerator(), sampleSharedChildStyleGeneratorAfterChildrenGeneratorBuilt(), 0D);
+    }
+
+    private double[] sampleSharedChildStyleGeneratorAfterChildrenGeneratorBuilt() {
+        buildChildrenGenerator();
+        return sampleSharedChildStyleGenerator(biome.getChildStyle());
+    }
+
+    private void buildChildrenGenerator() {
+        biome.getChildrenGenerator(new RNG(WORLD_SEED), CHILDREN_SIGNATURE, CHILD_SHRINK_FACTOR);
+    }
+
+    private double[] sampleUntouchedSharedChildStyleGenerator() {
+        return sampleSharedChildStyleGenerator(createSimplexStyle());
+    }
+
+    private double[] sampleSharedChildStyleGenerator(IrisGeneratorStyle childStyle) {
+        return sampleAtBlocks(childStyle.create(deriveSharedChildStyleSeed(), packData), SAMPLE_BLOCKS);
+    }
+
+    private static RNG deriveSharedChildStyleSeed() {
+        return IrisBiome.deriveChildStyleSeed(new RNG(WORLD_SEED), CHILDREN_SIGNATURE);
+    }
+
+    private static IrisBiome createBiomeWithSimplexChildStyle(IrisData packData) {
+        IrisBiome biome = new IrisBiome().setChildStyle(createSimplexStyle());
+        biome.setLoader(packData);
+        return biome;
+    }
+
+    private static IrisGeneratorStyle createSimplexStyle() {
+        return new IrisGeneratorStyle(NoiseStyle.SIMPLEX);
+    }
+}