test:

- Added decorator shared variance style test, expected to fail until the fix

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

core/src/test/java/art/arcane/iris/generation/decoration/IrisDecoratorVarianceGeneratorTest.java

@@ -0,0 +1,58 @@
+package art.arcane.iris.generation.decoration;
+
+import art.arcane.iris.generation.block.IrisBlockData;
+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.collection.KList;
+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 IrisDecoratorVarianceGeneratorTest {
+    private static final String SHARED_VARIANCE_STYLE_GENERATOR_BUG =
+            "IrisDecorator scales the shared variance style generator instead of its own. "
+                    + "Ref.: https://github.com/VolmitSoftware/Iris/issues/1251";
+    private static final long WORLD_SEED = 7L;
+    private static final double VARIANCE_ZOOM = 4D;
+    private static final double[][] SAMPLE_BLOCKS = {{1000D, -2000D}, {12.5D, -7.25D}, {-517D, 333D}};
+
+    private final IrisData packData = RunningEnginePackData.create();
+    private final IrisDecorator decorator = createDecoratorWithZoomedSimplexVariance();
+
+    @Rule
+    public final ExpectedToFailUntilFixedRule expectedFailures = new ExpectedToFailUntilFixedRule();
+
+    @ExpectedToFailUntilFixed(SHARED_VARIANCE_STYLE_GENERATOR_BUG)
+    @Test
+    public void doesBuildingTheVarianceGeneratorLeaveTheSharedVarianceStyleGeneratorUnscaled() {
+        assertArrayEquals(sampleUntouchedSharedVarianceStyleGenerator(), sampleSharedVarianceStyleGeneratorAfterVarianceBuilt(), 0D);
+    }
+
+    private double[] sampleSharedVarianceStyleGeneratorAfterVarianceBuilt() {
+        decorator.getVarianceGenerator(new RNG(WORLD_SEED), packData);
+        return sampleSharedVarianceStyleGenerator(decorator.getVariance());
+    }
+
+    private double[] sampleUntouchedSharedVarianceStyleGenerator() {
+        return sampleSharedVarianceStyleGenerator(createZoomedSimplexStyle());
+    }
+
+    private double[] sampleSharedVarianceStyleGenerator(IrisGeneratorStyle varianceStyle) {
+        return sampleAtBlocks(varianceStyle.create(decorator.deriveVarianceSeed(new RNG(WORLD_SEED), packData), packData), SAMPLE_BLOCKS);
+    }
+
+    private static IrisDecorator createDecoratorWithZoomedSimplexVariance() {
+        return new IrisDecorator().setPalette(new KList<IrisBlockData>()).setVariance(createZoomedSimplexStyle());
+    }
+
+    private static IrisGeneratorStyle createZoomedSimplexStyle() {
+        return new IrisGeneratorStyle(NoiseStyle.SIMPLEX).setZoom(VARIANCE_ZOOM);
+    }
+}