code coveage of CompletableFuture.supplyAsync code

1.I have 10 lines of code inside CompletableFuture.supplyAsync(() -> { } 2. junit test case is skipping that 10 lines of code. How can i cover those 10 lines

CompletableFuture.supplyAsync(() -> {

    // line 1
    // line 3
    ..
    ..
    ..
   // line 10


}