family.json

[
    {
        "id": 100,
        "url": "http://en.wikipedia.org/wiki/Salmonidae"
    }
]

mashup_expectation.json

[
    {
        "id": 1,
        "species": "Trout",
        "family": {
            "id": 100,
            "url": "http://en.wikipedia.org/wiki/Salmonidae"
        },
    },
    {
        "id": 2,
        "species": "AtlanticSalmon",
        "family": {
            "id": 100,
            "url": "http://en.wikipedia.org/wiki/Salmonidae"
        },
    }
]

species.json

[
    {
        "id": 1,
        "species": "Trout",
        "family_id": 100
    },
    {
        "id": 2,
        "species": "AtlanticSalmon",
        "family_id": 100
    }
]