JLS  chapter "*14.10 The assert Statement*" says:

-----------------JLS---------------------
An assert statement causes the enclosing top level class (if it exists) to be initialized, if it has not already been initialized (��12.4.1).

Discussion

Note that an assertion that is enclosed by a top-level interface does not cause initialization. stmt312

Usually, the top level class enclosing an assertion will already be initialized. However, if the assertion is located within a static nested class, it may be that the initialization has nottaken place.
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The following code is written to test assertion:
 "An assert statement causes the enclosing top level class (if it exists) to be initialized".

In this test "assert" statement is located within a static nested class:

===============Code================
class Test01 {
   static {
       stmt31201.i = 1;
   }

   static class Test01_1 {
       boolean test() {
           boolean enabled = false;
           assert enabled = true;
           return enabled;
       }
   }
}

public class stmt31201 {
   static int i = 0;

   public static void main(String args[]) {
       System.exit(run(args, System.out) + 95/*STATUS_TEMP*/);
   }

   public static int run(String argv[], PrintStream out) {
       out.println("i = " + i);
       Test01.Test01_1 obj = new Test01.Test01_1();
       obj.test();
       out.println("i = " + i);
       if (i != 1) {
           out.println("Top-level class hasn't been initialized");
           return 2;
       }
       return 0;
   }
}
===============Output============================
i = 0
i = 0
Top-level class hasn't been initialized
================================================

Hence the static initializer in Test_01 hasn't been executed.
It seems that realization contradicts the specification.