Certainly! Here's a test case generator for the given problem statement:

### Problem Statement: Insert Space in String

**Description**

Mr. Takahashi always writes "CODE FESTIVAL" as "CODEFESTIVAL", omitting the single space between "CODE" and "FESTIVAL". You are given a string `s` with exactly 12 letters. Your task is to output the string with a single space between the first 4 letters and the last 8 letters.

**Input**

A string `s` consisting of exactly 12 uppercase English letters.

**Output**

Print the string with a single space between the first 4 letters and the last 8 letters in the string `s`.

**Constraints**

- `s` contains exactly 12 uppercase English letters.

**Example**

_Input_
```
CODEFESTIVAL
```

_Output_
```
CODE FESTIVAL
```

_Input_
```
POSTGRADUATE
```

_Output_
```
POST GRADUATE
```

### Test Case Generator Code

Here is a Python script to generate test cases for this problem:

```python
import random
import string

def generate_random_string(length):
    return ''.join(random.choice(string.ascii_uppercase) for _ in range(length))

def tcgen():
    s = generate_random_string(12)
    return s

# Example of usage
for _ in range(5):
    s = tcgen()
    print(s)
```

This script generates a random string `s` of exactly 12 uppercase English letters, which fits the input constraints of the problem. Each time you run the `tcgen` function, it will provide a new valid test case. The example usage shows how to generate and print five test cases. 

You can adapt this script to generate as many test cases as needed for your testing purposes.