import * as mod from "https://deno.land/std@0.182.0/testing/snapshot.ts";
A snapshotting library.
The assertSnapshot
function will create a snapshot of a value and compare it
to a reference snapshot, which is stored alongside the test file in the
__snapshots__
directory.
// example_test.ts
import { assertSnapshot } from "https://deno.land/std@0.182.0/testing/snapshot.ts";
Deno.test("isSnapshotMatch", async function (t): Promise<void> {
const a = {
hello: "world!",
example: 123,
};
await assertSnapshot(t, a);
});
// __snapshots__/example_test.ts.snap
export const snapshot = {};
snapshot[`isSnapshotMatch 1`] = `
{
example: 123,
hello: "world!",
}
`;
Calling assertSnapshot
in a test will throw an AssertionError
, causing the
test to fail, if the snapshot created during the test does not match the one in
the snapshot file.
Updating Snapshots:
When adding new snapshot assertions to your test suite, or when intentionally
making changes which cause your snapshots to fail, you can update your snapshots
by running the snapshot tests in update mode. Tests can be run in update mode by
passing the --update
or -u
flag as an argument when running the test. When
this flag is passed, then any snapshots which do not match will be updated.
deno test --allow-all -- --update
Additionally, new snapshots will only be created when this flag is present.
Permissions:
When running snapshot tests, the --allow-read
permission must be enabled, or
else any calls to assertSnapshot
will fail due to insufficient permissions.
Additionally, when updating snapshots, the --allow-write
permission must also
be enabled, as this is required in order to update snapshot files.
The assertSnapshot
function will only attempt to read from and write to
snapshot files. As such, the allow list for --allow-read
and --allow-write
can be limited to only include existing snapshot files, if so desired.
Options:
The assertSnapshot
function optionally accepts an options object.
// example_test.ts
import { assertSnapshot } from "https://deno.land/std@0.182.0/testing/snapshot.ts";
Deno.test("isSnapshotMatch", async function (t): Promise<void> {
const a = {
hello: "world!",
example: 123,
};
await assertSnapshot(t, a, {
// options
});
});
You can also configure default options for assertSnapshot
.
// example_test.ts
import { createAssertSnapshot } from "https://deno.land/std@0.182.0/testing/snapshot.ts";
const assertSnapshot = createAssertSnapshot({
// options
});
When configuring default options like this, the resulting assertSnapshot
function will function the same as the default function exported from the
snapshot module. If passed an optional options object, this will take precedence
over the default options, where the value provded for an option differs.
It is possible to "extend" an assertSnapshot
function which has been
configured with default options.
// example_test.ts
import { createAssertSnapshot } from "https://deno.land/std@0.182.0/testing/snapshot.ts";
import { stripColor } from "https://deno.land/std@0.182.0/fmt/colors.ts";
const assertSnapshot = createAssertSnapshot({
dir: ".snaps",
});
const assertMonochromeSnapshot = createAssertSnapshot<string>(
{ serializer: stripColor },
assertSnapshot,
);
Deno.test("isSnapshotMatch", async function (t): Promise<void> {
const a = "\x1b[32mThis green text has had it's colours stripped\x1b[39m";
await assertMonochromeSnapshot(t, a);
});
// .snaps/example_test.ts.snap
export const snapshot = {};
snapshot[`isSnapshotMatch 1`] = `This green text has had it's colours stripped`;
Version Control:
Snapshot testing works best when changes to snapshot files are comitted alongside other code changes. This allows for changes to reference snapshots to be reviewed along side the code changes that caused them, and ensures that when others pull your changes, their tests will pass without needing to update snapshots locally.
Functions
Make an assertion that | |
Default serializer for |