Certainly! Given the problem statement, we need to generate test cases for a function that takes a 12-letter uppercase string and inserts a space between the first 4 letters and the last 8 letters. Here's a test case generator for this problem:

```python
import random
import string

def tcgen():
    # Generate a random string of exactly 12 uppercase letters
    s = ''.join(random.choices(string.ascii_uppercase, k=12))

    return s

# Example of generating a test case
if __name__ == "__main__":
    test_case = tcgen()
    print("Generated Test Case:", test_case)
    # Expected output
    expected_output = test_case[:4] + " " + test_case[4:]
    print("Expected Output:", expected_output)
```

### Explanation:
1. **Import necessary modules**: We import `random` for random number generation and `string` to get uppercase letters.
2. **Generate a random string**: Using `random.choices` with `string.ascii_uppercase`, we create a random string `s` of exactly 12 uppercase letters.
3. **Return the generated string**: The function returns this string `s`.

### Example usage:
When you run this script, it will generate a random 12-letter uppercase string and then print the expected output by inserting a space between the first 4 and the last 8 letters.

You can wrap this generator into a larger testing framework or use it to manually verify your solution to the problem.