I'll analyze the code for bugs and improvements, then write comprehensive test cases.

Code Analysis

Bugs Found:

1. Missing logger declaration - The code references logger.warn() but doesn't declare a logger instance

2. Potential null pointer in multipart - multipartSupplier could return empty list but the actual multipart handling might expect data

3. Content-Length calculation issue - For multipart requests, Content-Length is set before the multipart body is built

4. URL encoding in query string - Query parameters are being double-encoded (once in query() method context, once in building query string)

Improvements Needed:

1. Better error handling for malformed requests

2. Cookie parsing should handle special characters

3. Missing validation for HTTP method names

4. No support for testing streaming responses

5. Boundary generation could be more robust

Let me create comprehensive test cases with these fixes in mind:Now let me create a document with the bug analysis and improvement suggestions:I've completed a comprehensive analysis of the TestClient code. Here's what I've provided:

Key Findings:

Critical Bugs:

1. Missing logger - Referenced but never declared

2. Content-Length timing issue - Set before multipart body is built

3. Potential NullPointerException - InputStream could be null

Test Coverage:

The test suite includes 60+ test cases covering:

• All HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS)

• Headers, cookies, and query parameters

• Request bodies (string, bytes, JSON, form data)

• Multipart file uploads (single, multiple, with metadata)

• Response assertions (status, body, headers)

• Data extraction methods

• Edge cases and error handling

• Complete REST API and authentication workflows

Improvements Suggested:

• HTTP method validation

• Better cookie handling with attributes

• Timeout support

• Improved error messages

• Redirect following

• Streaming response support

• Debug logging

• Security validations (path traversal, header injection)

The test cases are written in English with clear comments and follow best practices for unit testing with JUnit 5 and Kotlin.