bcheidemann / deno-isolated-test-case

Run Deno tests in a separate isolated Deno process

Deno Isolated Test Case

Overview

Deno Isolated Test Case lets you run test cases in an isolated Deno process.

Motivation

Sometimes you need to ensure that other running tests are not interfering with the execution of your code, or visa versa. For instance, maybe your code pollutes the global scope, or maybe you need to make assertions about memory usage. Whatever your reason, Deno Isolated Test Case lets you run your test case in a separate process, while still being able to use standard assertions like assertEquals.

Usage

In your test file, you can add an isolated test case at the top level as follows:

import { isolatedTestCase } from "@bcheidemann/deno-isolated-test-case";

isolatedTestCase("test name", () => {
  // Your test case
});

Permissions

The minimum permissions required to run an isolated test case are --allow-env=DENO_ISOLATED_TEST_CASE_CTX --allow-net --allow-run=deno.

Options

Option	Description
assertFailure	If truthy, the test is expected to fail. A function can be passed to assert against the error.
denoFlags	Flags to pass to deno run.

Limitations

Top Level Only

Test cases must be at the top level and run unconditionally. They can not be nested in describe blocks or as steps of other Deno.test cases.

Snapshot Assertions

Since your test runs in an isolated Deno process, it will not be aware of other snapshots in your test file. If you assert snapshots across multiple tests, only the last tests snapshots will be captured. The solution is to manually override the snapshot file name to be unique per test.

Error Stack Traces

Deno for whatever reason doesn't allow us to override the Error.stack property. In order to ensure useful stack traces in our tests, we manually append the stack trace to the error message. This ensures stack traces are reported properly in tests, but it means that the message includes the stack trace.