Function assert_all_sessions_from_provider 

pub fn assert_all_sessions_from_provider(
    json: &Value,
    expected_provider: &str,
) -> Result<()>

Assert that all sessions in the list come from the expected provider.

Example

let json = json!({
    "content": {
        "sessions": [
            {"source": "claude_code"},
            {"source": "claude_code"}
        ]
    }
});

assertions::assert_all_sessions_from_provider(&json, "claude_code").unwrap();