assert-json-diff

This crate includes an assert macro for comparing two JSON values. It is designed to give much more helpful error messages than the standard assert_eq!. It basically does a diff of the two objects and tells you the exact differences. This is useful when asserting that two large JSON objects are the same.

It uses the serde_json::Value type to represent JSON.

Example

#[macro_use]
extern crate assert_json_diff;
#[macro_use]
extern crate serde_json;

// probably with #[test] attribute
fn some_test() {
    let a = json!({
        "data": {
            "users": [
                {
                    "id": 1,
                    "country": {
                        "name": "Denmark"
                    }
                },
                {
                    "id": 24,
                    "country": {
                        "name": "Denmark"
                    }
                }
            ]
        }
    });

    let b = json!({
        "data": {
            "users": [
                {
                    "id": 1,
                    "country": {
                        "name": "Sweden"
                    }
                },
                {
                    "id": 2,
                    "country": {
                        "name": "Denmark"
                    }
                }
            ]
        }
    });

    assert_json_eq!(actual: a, expected: b)
}

This will panic with the error message:

json atoms at path ".data.users[0].country.name" are not equal:
    expected:
        "Sweden"
    actual:
        "Denmark"

json atoms at path ".data.users[1].id" are not equal:
    expected:
        2
    actual:
        24

Additional data

It allows extra data in actual but not in expected. That is so you can verify just a part of the JSON without having to specify the whole thing. For example this test passes:

#[macro_use]
extern crate assert_json_diff;
#[macro_use]
extern crate serde_json;

// probably with #[test] attribute
fn some_test() {
    assert_json_eq!(
        actual: json!({
            "a": { "b": 1 },
        }),
        expected: json!({
            "a": {},
        })
    )
}

However expected cannot contain additional data so this test fails:

#[macro_use]
extern crate assert_json_diff;
#[macro_use]
extern crate serde_json;

// probably with #[test] attribute
fn some_test() {
    assert_json_eq!(
        actual: json!({
            "a": {},
        }),
        expected: json!({
            "a": { "b": 1 },
        })
    )
}

That will print

json atom at path ".a.b" is missing from expected

The macro

The assert_json_eq! macro can be called with or without typing actual: and expected:

#[macro_use]
extern crate assert_json_diff;
#[macro_use]
extern crate serde_json;

// probably with #[test] attribute
fn some_test() {
    assert_json_eq!(
        actual: json!(true),
        expected: json!(true)
    )
}

// probably with #[test] attribute
fn some_other_test() {
    assert_json_eq!(
        json!(true),
        json!(true)
    )
}

The version that includes actual: and expected: is preferred because it makes it very clear which is which and there which can contain additional data

License: MIT