Sure, here's a test case generator for the given problem "The Humans Braving the Invaders":

```python
import random

def generate_test_case():
    # Generate a random number of data sets, not more than 3
    num_datasets = random.randint(1, 3)
    test_case = []
    
    for _ in range(num_datasets):
        # Generate Q (1 ≤ Q ≤ 100000) and L (1 ≤ L ≤ 10^9)
        Q = random.randint(1, 100000)
        L = random.randint(1, 10**9)
        test_case.append(f"{Q} {L}")
        
        queries = []
        for _ in range(Q):
            query_type = random.randint(0, 4)
            
            if query_type == 0:
                queries.append(f"0")
            elif query_type == 1:
                d = random.randint(1, 10**9)
                queries.append(f"1 {d}")
            elif query_type == 2:
                k = random.randint(1, 10**9)
                queries.append(f"2 {k}")
            elif query_type == 3:
                x = random.randint(0, L)
                r = random.randint(0, 10**9)
                queries.append(f"3 {x} {r}")
            elif query_type == 4:
                k = random.randint(1, 10**9)
                queries.append(f"4 {k}")
        
        test_case.extend(queries)
    
    # Append the ending zeroes to signify the end of input
    test_case.append("0 0")
    
    return test_case

# Example of how to use the test case generator
test_case = generate_test_case()
for line in test_case:
    print(line)
```

### Explanation:
1. **Number of Datasets**: The generator first determines how many datasets to generate (between 1 and 3).
2. **Q and L**: For each dataset, it generates `Q` (number of queries, between 1 and 100000) and `L` (field length, between 1 and 10^9).
3. **Queries**: For each query, it randomly selects a query type (0 to 4) and generates appropriate parameters:
   - **Type 0**: No additional parameters.
   - **Type 1**: Generates a random `d` (1 to 10^9).
   - **Type 2**: Generates a random `k` (1 to 10^9).
   - **Type 3**: Generates a random `x` (0 to `L`) and a random `r` (0 to 10^9).
   - **Type 4**: Generates a random `k` (1 to 10^9).
4. **End of Input**: Finally, it appends "0 0" to signify the end of input.

This generator ensures that the generated test cases conform to the constraints provided in the problem statement.