test: characterize default content

Pin the singleton ABI and exact built-in factory, material, and remap registrations.

src/test/java/codechicken/microblock/DefaultContentCharacterizationTest.java

@@ -0,0 +1,44 @@
+package codechicken.microblock;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+
+import org.junit.jupiter.api.Test;
+import org.objectweb.asm.Type;
+
+class DefaultContentCharacterizationTest {
+
+    @Test
+    void keepsTheFacadeAndCompanionSurface() throws Exception {
+        assertSingletonType(DefaultContent.class, true);
+        assertSingletonType(DefaultContent$.class, false);
+
+        assertArrayEquals(new Class<?>[0], DefaultContent.class.getInterfaces());
+        assertArrayEquals(new Class<?>[0], DefaultContent$.class.getInterfaces());
+        assertEquals(0, DefaultContent.class.getFields().length);
+
+        Field module = DefaultContent$.class.getField("MODULE$");
+        assertSame(DefaultContent$.class, module.getType());
+        assertTrue(Modifier.isStatic(module.getModifiers()));
+        assertTrue(Modifier.isFinal(module.getModifiers()));
+        assertSame(DefaultContent$.MODULE$, module.get(null));
+    }
+
+    private static void assertSingletonType(Class<?> type, boolean staticMethod) {
+        assertTrue(Modifier.isPublic(type.getModifiers()));
+        assertTrue(Modifier.isFinal(type.getModifiers()));
+
+        Method[] methods = type.getDeclaredMethods();
+        assertEquals(1, methods.length);
+        assertEquals("load()V", methods[0].getName() + Type.getMethodDescriptor(methods[0]));
+        assertTrue(Modifier.isPublic(methods[0].getModifiers()));
+        assertEquals(staticMethod, Modifier.isStatic(methods[0].getModifiers()));
+        assertEquals(0, methods[0].getDeclaredAnnotations().length);
+    }
+}