Tests

Writing Tests

Deno have its own Test library, so there is no need to use external tools like Jest or others.

Tests structures

Simple test

Deno.test('', () => {});

Test steps

Deno also supports test steps, which allow you to break down tests into smaller, manageable parts.

Deno.test("database operations", async (t) => {
    using db = await openDatabase();
    await t.step("insert user", async () => {
        // Insert user logic
    });
    await t.step("insert book", async () => {
        // Insert book logic
    });
});

Assertions

Deno provides a function assertEqual and others for asserting expected values.

But it also provides an assert function like Jest expect.

Running tests

Run deno test without a file name or directory name, this subcommand will automatically find and execute all tests in the current directory (recursively).

# Run all tests in the current directory and all sub-directories
deno test

# Run all tests in the util directory
deno test util/

# Run just my_test.ts
deno test my_test.ts

# Run test modules in parallel
deno test --parallel

# Pass additional arguments to the test file that are visible in `Deno.args`
deno test my_test.ts -- -e --foo --bar

# Provide permission for deno to read from the filesystem, which is necessary
# for the final test above to pass
deno test --allow-read my_test.ts