Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@frontend/__tests__/tsconfig.json`:
- Around line 4-8: Remove the "@testing-library/jest-dom" entry from the
tsconfig "types" array because it causes TS2688 with v6+; instead rely on the
import in jest.setup.ts (configured via setupFilesAfterEnv) which already
provides the globals, so edit the "types" array to omit
"@testing-library/jest-dom" and keep "jest" and "node" intact.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@frontend/__tests__/a11y/components/RecentPullRequests.a11y.test.tsx`:
- Around line 56-57: The test fixture in RecentPullRequests.a11y.test.tsx has an
inconsistent PR object with state: 'open' but a mergedAt timestamp; update the
fixture to be realistic by either setting state to 'merged' (so mergedAt remains
valid) or removing the mergedAt field if the PR should be open—locate the PR
object in the RecentPullRequests.a11y.test.tsx test case and adjust the state or
mergedAt accordingly to keep the fixture consistent with GraphQL DateTime ISO
string conventions.

In `@frontend/__tests__/a11y/components/SingleModuleCard.a11y.test.tsx`:
- Around line 60-61: The fixture mockModule uses startedAt as a numeric Unix
timestamp while endedAt is an ISO string; update startedAt to an ISO 8601 string
to match endedAt (e.g., new Date(1704067200 * 1000).toISOString()) so both
timestamp fields use the same type expected by the Module/GraphQL DateTime
serialization; ensure you update any tests that rely on numeric timestamps to
use the ISO string form as well.

In `@frontend/__tests__/unit/components/SingleModuleCard.test.tsx`:
- Around line 113-114: The test fixture in SingleModuleCard.test.tsx uses mixed
date formats: startedAt is a numeric Unix timestamp while endedAt is an ISO
string; update the fixture so both DateTime fields are ISO 8601 strings (e.g.,
set startedAt to new Date(1704067200 * 1000).toISOString() or an equivalent ISO
string) so startedAt and endedAt are consistent with GraphQL DateTime
serialization and the component's runtime expectations.

In `@frontend/__tests__/unit/components/SnapshotCard.test.tsx`:
- Around line 52-60: The test is using "0 as unknown as string" to simulate
missing dates which hides intent; update the two calls to render/rerender of
SnapshotCard to pass an explicit missing sentinel (prefer undefined or null,
e.g. startAt={undefined} and endAt={undefined}) instead of the type-coerced 0,
keeping the same asserts; if TypeScript complaints, adjust the test props by
casting only the prop (e.g. startAt={undefined as unknown as string} or widen
defaultProps type) so you change lines that set startAt/endAt in the render and
rerender calls for SnapshotCard and leave formatDate and expectations unchanged.