test: characterize corner microblock traits

src/test/java/codechicken/microblock/CornerMicroblockTraitsCharacterizationTest.java

@@ -0,0 +1,93 @@
+package codechicken.microblock;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Base64;
+import java.util.Objects;
+import java.util.Scanner;
+
+import org.junit.jupiter.api.Test;
+
+/** Executes corner-trait forwarders compiled against the untouched Scala implementation. */
+class CornerMicroblockTraitsCharacterizationTest {
+
+    @Test
+    void packsSupportedCornersThroughTheVirtualShapeSetterExactlyOnce() throws Exception {
+        Fixture f = new Fixture();
+        assertEquals(29, f.part.material());
+        assertEquals(0, f.part.shape());
+        int writes = 0;
+        for (int size = 1; size <= 7; size++) {
+            for (int corner = 0; corner < 8; corner++) {
+                f.part.setShape(size, corner + 7);
+                byte expected = (byte) (size * 16 + corner);
+                assertEquals(expected, f.part.shape());
+                assertEquals(expected, f.get("writtenShape"));
+                assertEquals(++writes, f.get("writes"));
+                assertEquals(size, f.part.getSize());
+                assertEquals(corner + 7, f.corner.getSlot());
+                assertEquals(1 << (corner + 7), f.corner.getSlotMask());
+                assertEquals(29, f.part.material());
+            }
+        }
+    }
+
+    @Test
+    void preservesTruncationAndOutOfRangeSlotBitsWithoutValidation() throws Exception {
+        Fixture f = new Fixture();
+        int[][] cases = { { 1, 6, -1, -1, 22 }, { 8, 7, -128, -8, 7 }, { 16, 7, 0, 0, 7 }, { 0, 23, 16, 1, 7 },
+                { -1, 14, -9, -1, 14 }, { Integer.MAX_VALUE, Integer.MIN_VALUE, -7, -1, 16 } };
+        for (int[] value : cases) {
+            f.part.setShape(value[0], value[1]);
+            assertEquals((byte) value[2], f.part.shape());
+            assertEquals(value[3], f.part.getSize());
+            assertEquals(value[4], f.corner.getSlot());
+        }
+        assertEquals(cases.length, f.get("writes"));
+    }
+
+    @Test
+    void slotDecodingUsesTheVirtualGetterAndKeepsIntegerOverflow() throws Exception {
+        Fixture f = new Fixture();
+        f.set("overrideShape", boolean.class, true);
+        int[][] cases = { { -8, -1 }, { 0, 7 }, { 25, 32 }, { Integer.MAX_VALUE, Integer.MIN_VALUE + 6 } };
+        int reads = 0;
+        for (int[] value : cases) {
+            f.set("selectedShape", int.class, value[0]);
+            assertEquals(value[1], f.corner.getSlot());
+            assertEquals(++reads, f.get("reads"));
+            assertEquals(1 << value[1], f.corner.getSlotMask());
+            assertEquals(++reads, f.get("reads"));
+        }
+        assertEquals(0, f.get("writes"));
+        assertEquals(0, f.part.shape());
+    }
+
+    private static final class Fixture extends ClassLoader {
+
+        final Microblock part;
+        final CornerMicroblock corner;
+
+        Fixture() throws Exception {
+            super(Microblock.class.getClassLoader());
+            InputStream input = Objects
+                    .requireNonNull(getClass().getResourceAsStream("/compat/ReferenceScalaCornerMicroblock.class.b64"));
+            byte[] bytes;
+            try (Scanner scanner = new Scanner(input, StandardCharsets.US_ASCII.name()).useDelimiter("\\A")) {
+                bytes = Base64.getMimeDecoder().decode(scanner.next());
+            }
+            part = (Microblock) defineClass(null, bytes, 0, bytes.length).getConstructor().newInstance();
+            corner = (CornerMicroblock) part;
+        }
+
+        Object get(String name) throws Exception {
+            return part.getClass().getMethod(name).invoke(part);
+        }
+
+        void set(String name, Class<?> type, Object value) throws Exception {
+            part.getClass().getMethod(name + "_$eq", type).invoke(part, value);
+        }
+    }
+}