- fix: NullPointerException when the config class of mod updated

- alter: better test code in `common/src/test`, `neoforge/src/test` and `fabric/src/test`, run `Test Minecraft Client(:fabric)` or `Test Minecraft Client(:neoforge)` for testing

common/build.gradle

@@ -1,3 +1,7 @@
+plugins {
+    id 'java'
+}
+
 architectury {
     common(rootProject.enabled_platforms.split(","))
 }
@@ -21,3 +25,16 @@ publishing {
         // Add repositories to publish to here.
     }
 }
+
+configurations {
+    testOutput.extendsFrom(testImplementation)
+}
+
+tasks.register('testJar', Jar) {
+    from sourceSets.test.output
+    archiveClassifier = 'tests'
+}
+
+artifacts {
+    testOutput testJar
+}