added command line to create migrations

src/test/java/jef/model/EntityDefaultConstructorCheckerTest.java

@@ -0,0 +1,39 @@
+package jef.model;
+
+import jef.model.annotations.Id;
+import jef.serializable.SerializableObject;
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class EntityDefaultConstructorCheckerTest {
+    @Test
+    public void test0ArgConstructor() {
+        var mb = new ModelBuilder();
+        EntityDefaultConstructorChecker.checkEntity(mb.entity(TestClass0Arg.class));
+        assertTrue(true);
+    }
+
+    @Test
+    public void testNon0ArgConstructor() {
+        var mb = new ModelBuilder();
+        var ex = assertThrows(ModelException.class, () -> EntityDefaultConstructorChecker.checkEntity(mb.entity(TestClassNon0Arg.class)));
+        assertEquals("Class 'TestClassNon0Arg' does not have a default constructor!", ex.getMessage());
+    }
+
+    @NoArgsConstructor
+    public static class TestClass0Arg extends SerializableObject {
+        @Id
+        public int i = 1;
+    }
+
+    @AllArgsConstructor
+    public static class TestClassNon0Arg extends SerializableObject {
+        @Id
+        public int i = 1;
+    }
+}