Function json_contains 

pub fn json_contains(actual: &Value, expected: &Value) -> Result<(), String>

Checks if actual contains all fields from expected.

Returns Ok(()) if matching succeeds, or Err(path) where path is the JSON path to the first mismatch.

Matching Rules

• Objects: All keys in expected must exist in actual with matching values. Extra keys in actual are ignored.
• Arrays: Must match exactly (same length, same elements in order).
• Primitives: Must be equal.

Example

use fastapi_core::testing::json_contains;
use serde_json::json;

// Partial match succeeds - actual has extra "email" field
let actual = json!({"id": 1, "name": "Alice", "email": "alice@example.com"});
let expected = json!({"name": "Alice"});
assert!(json_contains(&actual, &expected).is_ok());

// Mismatch fails
let expected = json!({"name": "Bob"});
assert!(json_contains(&actual, &expected).is_err());