streamtest

streamtest is a library for testing streams in Deno. Provides helper functions that make it easier to test streams with various scenarios and assertions.

Inspired by the test helpers in RxJS.

Define stream scenarios

A simple string series can be used to define values to be enqueued into a stream and events such as closes and errors.

Series format

The following characters are available in the series:

\x20 : Space is ignored. Used to align columns.
- : Advance 1 tick.
| : Close the stream.
! : Cancel the stream.
# : Abort the stream.
(...) : Groups characters. It does not advance ticks inside. After closing ), advance 1 tick.
Characters with keys in values will have their values enqueued to the stream, and then advance 1 tick.
Other characters are enqueued into the stream as a single character, and then advance 1 tick.

Example for Series format

Series: " ---A--B(CD)--|"
Values: { A: "foo" }

Waits 3 ticks.
"foo" is enqueued and waits 1 tick.
Waits 2 ticks.
"B" is enqueued and waits 1 tick.
"C" is enqueued, "D" is enqueued and waits 1 tick.
Waits 2 ticks.
Close the stream.

API Reference

`testStream`

Define a block to test streams. TestStreamHelper is passed to the function specified for testStream, which has helper functions available only within that function.

import {
  testStream,
  type TestStreamHelper,
} from "https://deno.land/x/streamtest/test_stream.ts";

Deno.test("MyTransformer", async () => {
  await testStream(async (helper: TestStreamHelper) => {
    // ... test logic using helper.assertReadable, helper.readable, and helper.run ...
  });
});

`readable` helper

Creates a ReadableStream with the specified series.

import { testStream } from "https://deno.land/x/streamtest/test_stream.ts";

Deno.test("readable", async () => {
  await testStream(async ({ readable }) => {
    const abortReason = new Error("abort");
    const values = {
      A: "foo",
      B: "bar",
      C: "baz",
    } as const;

    // "a" ..sleep.. "b" ..sleep.. "c" ..sleep.. close
    const characterStream = readable("a--b--c--|");

    // ..sleep.. "foo" ..sleep.. "bar" ..sleep.. "baz" and close
    const stringStream = readable("   --A--B--(C|)", values);

    // "0" ..sleep.. "1" ..sleep.. "2" ..sleep.. abort
    const errorStream = readable("    012#", undefined, abortReason);

    // Now you can use the `*Stream` in your test logic.
  });
});

`assertReadable` helper

Asserts that the readable stream matches the specified series.

import { testStream } from "https://deno.land/x/streamtest/test_stream.ts";
import { UpperCase } from "https://deno.land/x/streamtest/examples/upper_case.ts";

Deno.test("assertReadable", async () => {
  await testStream(async ({ assertReadable, readable }) => {
    const abortReason = new Error("abort");
    const values = {
      A: "foo",
      B: "bar",
      C: "baz",
    } as const;

    const stream = readable("--A--B--C--#", values, abortReason);
    const expectedSeries = " --A--B--C--#";
    const expectedValues = {
      A: "FOO",
      B: "BAR",
      C: "BAZ",
    };

    const actual = stream.pipeThrough(new UpperCase());

    await assertReadable(actual, expectedSeries, expectedValues, abortReason);
  });
});

`run` helper

Process the test streams inside the run block.

import { assertEquals } from "https://deno.land/std/assert/assert_equals.ts";
import { testStream } from "https://deno.land/x/streamtest/test_stream.ts";
import { UpperCase } from "https://deno.land/x/streamtest/examples/upper_case.ts";

Deno.test("run", async () => {
  await testStream(async ({ run, readable }) => {
    const stream = readable("--a--b--c--|");

    const actual = stream.pipeThrough(new UpperCase());

    await run([actual], async (actual) => {
      const reader = actual.getReader();

      assertEquals(await reader.read(), { value: "A", done: false });
      assertEquals(await reader.read(), { value: "B", done: false });
      assertEquals(await reader.read(), { value: "C", done: false });
      assertEquals(await reader.read(), { value: undefined, done: true });

      reader.releaseLock();
    });
  });
});

License

This library is licensed under the MIT License. See the LICENSE file for details.