Sure! Here is a test case generator for the "Constellation" problem in Python:

```python
import random

def generate_star_coordinates(num_stars, max_coordinate=1000000):
    stars = set()
    while len(stars) < num_stars:
        x = random.randint(0, max_coordinate)
        y = random.randint(0, max_coordinate)
        stars.add((x, y))
    return list(stars)

def tcgen():
    datasets = []
    
    num_datasets = random.randint(1, 5)
    for _ in range(num_datasets):
        # Generate the constellation
        m = random.randint(1, 200)
        constellation = generate_star_coordinates(m)
        
        # Generate the photo with the constellation and additional stars
        n = random.randint(m, 1000)
        photo = generate_star_coordinates(n)
        
        # Ensure the constellation is a subset of the photo
        photo[:m] = constellation
        
        # Shuffle the photo to add randomness
        random.shuffle(photo)
        
        datasets.append((m, constellation, n, photo))
    
    return datasets

def format_dataset(dataset):
    m, constellation, n, photo = dataset
    result = []
    
    result.append(str(m))
    for star in constellation:
        result.append(f"{star[0]} {star[1]}")
    
    result.append(str(n))
    for star in photo:
        result.append(f"{star[0]} {star[1]}")
    
    return "\n".join(result)

def generate_input():
    datasets = tcgen()
    input_str = "\n".join(format_dataset(dataset) for dataset in datasets)
    input_str += "\n0"  # End of input indicator
    return input_str

# Example of generating an input
print(generate_input())
```

### Explanation:
1. **`generate_star_coordinates(num_stars, max_coordinate=1000000)`**:
    - Generates a set of unique star coordinates within the specified range.
    
2. **`tcgen()`**:
    - Generates up to 5 datasets (between 1 and 5).
    - For each dataset:
        - It generates the constellation coordinates (`m` stars).
        - It generates the photo with `n` stars where `n >= m`.
        - Ensures the constellation is included in the photo.
        - Randomizes the order of stars in the photo for added complexity.
        
3. **`format_dataset(dataset)`**:
    - Formats a single dataset to match the input format required by the problem statement.

4. **`generate_input()`**:
    - Combines multiple datasets into a single string, including the end-of-input indicator `0`.

This test case generator creates diverse and complex inputs that conform to the problem's input constraints, ensuring robust testing for the solution.