In-Memory Key-Value Database CRUD Implementation

openai Implement an in-memory database that supports basic CRUD operations. The database should support the following features: Insert operation: Insert a record into the database, which contains a key and a corresponding value. Query operation: Query the value from the database based on the key. If the key does not exist, return null. Update operation: Update the value of a record in the database based on the key. If the key does not exist, throw an exception. Delete operation: Delete a record from the database based on the key. Please implement the above features using Python and design appropriate test cases to verify the correctness of the functionality. Input: Specific operations and data Output: Database state after each operation Example Input insert key1 value1 query key1 update key1 value2 query key1 delete key1 query key1