Example

Consider the following pydantic objects:

class Author(BaseModel):
given_name: str
surname: str


class Book(BaseModel):
    title: str
    published_at: datetime
    author: Author

A json schema for these is built from a dict that pydantic generates via the model_json_schema method and will look like this:

expected_book_schema = {
    "$defs": {
        "Author": {
            "properties": {
                "given_name": {"title": "Given Name", "type": "string"},
                "surname": {"title": "Surname", "type": "string"},
            },
            "required": ["given_name", "surname"],
            "title": "Author",
            "type": "object",
        }
    },
    "properties": {
        "title": {"title": "Title", "type": "string"},
        "published_at": {
            "format": "date-time",
            "title": "Published At",
            "type": "string",
        },
        "author": {"$ref": "#/$defs/Author"},
    },
    "required": ["title", "published_at", "author"],
    "title": "Book",
    "type": "object",
}

Now suppose the you don’t really care about the formatting/cases/wording of the title as it doesn’t affect the program. You care about the other stuff in your test: that the keys are correct and that they serialise to the correct type.

So we change our expected dictionary for a similarity match:

expected_book_schema = {
    "$defs": {
        "Author": {
            "properties": {
                "given_name": {"title": str, "type": "string"},
                "surname": {"title": str, "type": "string"},
            },
            "required": ["given_name", "surname"],
            "title": str,
            "type": "object",
        }
    },
    "properties": {
        "title": {"title": str, "type": "string"},
        "published_at": {
            "format": "date-time",
            "title": str,
            "type": "string",
        },
        "author": {"$ref": "#/$defs/Author"},
    },
    "required": ["title", "published_at", "author"],
    "title": str,
    "type": "object",
}

HINT: all titles have been replaced with a str type.

And so let’s look at our test:

def test_book_schema():
    assert similar_dict(Book.model_json_schema(), expected_book_schema)

This test will succeed, despite that it’s not an exact match for the Schema definition.