test: characterize the package objects

Each holds one member, a logger alias for its proxy's logger. Everything goes
through reflection because 'package' is a Java keyword and cannot appear as a
type name in Java source, which is also why these two classes have no Java
form at all.

The plain-JVM half pins the shape and that the alias reads the proxy's var
rather than holding anything, so it reports null before preInit. The Forge
server half pins the part that matters for what comes next: after preInit each
alias returns the very instance its proxy holds, adding nothing.

123 plain-JVM tests, 23 Forge server tests.

src/test/java/codechicken/multipart/PackageObjectCharacterizationTest.java

@@ -0,0 +1,55 @@
+package codechicken.multipart;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+
+import org.apache.logging.log4j.Logger;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Both package objects hold one member, a {@code logger} alias for their proxy's logger.
+ * <p>
+ * Everything here goes through reflection because {@code package} is a Java keyword:
+ * {@code codechicken.multipart.package} cannot be written as a type name in Java source at all. That is not a style
+ * choice, it is the reason these two classes have no Java form.
+ */
+class PackageObjectCharacterizationTest {
+
+    @Test
+    void bothPackageObjectsExposeAStaticLoggerAccessor() throws Exception {
+        for (String name : new String[] { "codechicken.multipart.package", "codechicken.microblock.package" }) {
+            Method logger = Class.forName(name).getDeclaredMethod("logger");
+
+            assertSame(Logger.class, logger.getReturnType(), name);
+            assertTrue(Modifier.isPublic(logger.getModifiers()), name);
+            assertTrue(Modifier.isStatic(logger.getModifiers()), name);
+        }
+    }
+
+    @Test
+    void bothCarryACompanionSingleton() throws Exception {
+        for (String name : new String[] { "codechicken.multipart.package$", "codechicken.microblock.package$" }) {
+            Class<?> companion = Class.forName(name);
+
+            assertSame(companion, companion.getField("MODULE$").getType(), name);
+        }
+    }
+
+    /**
+     * The alias reads the proxy's var rather than holding anything, so before preInit has run it reports null instead
+     * of failing. The Forge server suite asserts the other half, that after preInit it is the very same instance.
+     */
+    @Test
+    void theAliasReportsWhateverTheProxyHoldsAndIsNullBeforePreInit() throws Exception {
+        assertNull(invokeLogger("codechicken.multipart.package"));
+        assertNull(invokeLogger("codechicken.microblock.package"));
+    }
+
+    private static Object invokeLogger(String name) throws Exception {
+        return Class.forName(name).getDeclaredMethod("logger").invoke(null);
+    }
+}