mismatched

mismatched is a Typescript-based assertion and matcher framework, with a sophisticated compositional approach. Available at https://github.com/rickmugridge/mismatched.

mismatched can be used:

• for mismatched assertions with assertThat().
• as matcher for arguments in mocked calls in thespian
• for data validation with validateThat()

For latest changes, see What is New.

Also see:

• FAQ
• assertThat()
• validateThat()
• matchers
• PrettyPrinter
• Diff Tree
• How Mismatch Works

Example Assertions:

Here's a few simple examples of assertions (all these examples are in the examples directory here:

describe("Object-matching Examples", () => {
    const actual = {name: "hamcrest", address: {number: 3, street: "Oak St", other: [1, 2]}};

    it('Full object match', () => {
        assertThat(actual)
            .is({name: "hamcrest", address: {number: 3, street: "Oak St", other: [1, 2]}});
    });

    describe("Partial object match", () => {
        it('Do not care about one field', () => {
            assertThat(actual)
                .is({
                    name: "hamcrest",
                    address: {number: 3, street: "Oak St", other: match.any()}
                });
        });

        it('Matching optionally on several fields', () => {
            assertThat(actual)
                .is({
                    name: match.anyOf(["hamcrest", "tsDiffMatcher"]),
                    address: {
                        number: match.number.greater(0),
                        street: "Oak St",
                        other: match.ofType.array()
                    }
                });
        });
    });
});

We can see above that:

• We can specify an object as the match, and a suitable matcher will be constructed automatically
• We can use matchers at arbitrary points in the matching object (or array or at the top level)
  • Eg, because we don't care about some part of it (eg, a field which is randomly generated)
  • Eg, because we don't need to be too specific (some number, some array)

when matching fails, and the changes are minor, it provides feedback as a diff tree (looks to be related to a Haskell tree-diff). Eg:

When the address.number was 3 but was expected to be 4.

Matchers

There are many built-in matchers. See Matchers. This includes a section on writing custom matchers.

Displaying the results of mismatches

We aim to provide useful output when a match fails. PrettyPrinter does this.

The results are provided as a JS object, which shows what matched and what didn't in a diff tree. It does not display it in JSON format. Instead, it is displayed as plain JS, so that it's easy to copy parts of it if a test is not right.

It aims to lay out the JS object/value to make it convenient to read. It tries to strike a balance between all being on one line and being spread out over many lines. Either extreme can make it difficult to read.

It allows for custom renderers.

validateThat()

validateThat() is intended for validating data received.

Here's a simple example of validations (see the micro tests for individual matchers for other examples):

    it("validateThat():", () => {
            const validationResult = validateThat({f: 2, g: true})
                .satisfies({f: match.ofType.number(), g: match.ofType.boolean()});
            assertThat(validationResult.passed()).is(true);
    });

See validateThat() for further details.

Automated tests for mismatched itself

There are many unit (micro) tests. To run:

  npm test

There are also property tests. To run:

   npm run prop-test

See Testing Mismatched with Property Tests for further details.