Sure, let's write a test case generator for the "Zero AND Subsets" problem. This generator will create a random number of elements in the multiset, generate random integers within the specified range, and return them in the required format.

Here's the Python test case generator:

```python
import random

def tcgen():
    # Constraints
    N = random.randint(1, 10**5)
    A = [random.randint(0, 2**20 - 1) for _ in range(N)]
    
    return N, A

# Example of using the test case generator
if __name__ == "__main__":
    N, A = tcgen()
    print(N)
    print(" ".join(map(str, A)))
```

This code snippet does the following:
1. Randomly selects `N`, the number of elements in the multiset, within the range \([1, 10^5]\).
2. Generates a list `A` of `N` integers, each randomly selected from the range \([0, 2^{20} - 1]\).
3. Returns the values of `N` and `A`.

To see the generated test case, you can run the script. It prints the number of elements and the elements themselves in the format required by the problem statement.