Sure! To generate test cases for the "All Numbers Lead to 6174" problem, we need to generate valid four-digit numbers (including those with leading zeros). We also need to handle the special case where all digits are the same, which should result in an output of "NA".

Here's a Python test case generator for this problem:

```python
import random

def generate_four_digit_number():
    return random.randint(0, 9999)

def format_number(N):
    return f"{N:04}"

def tcgen(num_datasets=10):
    datasets = []
    for _ in range(num_datasets):
        N = generate_four_digit_number()
        datasets.append(format_number(N))
    
    # Adding the end of input line '0000'
    datasets.append("0000")
    
    return datasets

# Example usage
if __name__ == "__main__":
    test_cases = tcgen(10)
    for case in test_cases:
        print(case)
```

This generator creates a specified number of test cases (default is 10) where each test case is a four-digit number formatted as a string with leading zeros if necessary. It also appends the terminating line "0000".

### Explanation:
- `generate_four_digit_number`: Generates a random integer between 0 and 9999.
- `format_number`: Formats the number to ensure it is a four-digit string by adding leading zeros if needed.
- `tcgen`: Generates a list of test cases and appends the terminating "0000" line.

Feel free to adjust the number of datasets by passing a different value to the `tcgen` function when you call it. This will give you a variety of four-digit numbers to test the solution for the given problem.