Improve test coverage to ~100% for @azure/core-rest-pipeline

[deyaaeldeen]

Changes

New test files

• createPipelineFromOptions.spec.ts (browser + node)
• file.spec.ts (browser + node)
• policyFactories.spec.ts (node)
• tokenCycler.spec.ts
• userAgent.spec.ts
• userAgentPolicy.spec.ts

Expanded existing tests

• bearerTokenAuthenticationPolicy.spec.ts: CAE challenges, token refresh, error recovery
• auxiliaryAuthenticationHeaderPolicy.spec.ts: multi-tenant auth flows
• fetchHttpClient.spec.ts: abort, streaming, progress reporting
• nodeHttpClient.spec.ts: abort, streaming, upload/download progress
• pipeline.spec.ts: policy ordering, request overrides
• tracingPolicy.spec.ts: span attributes, error recording
• ndJsonPolicy.spec.ts: edge cases
• setClientRequestIdPolicy.spec.ts: header setting

Test quality improvements

• Replaced downloadCalled/uploadCalled/bodySent/listenerRemoved flags with vi.fn()
• Replaced isCallbackCalled/getTokenRequests counters with vi.fn()
• Removed inverted try/catch (success assertions) in favor of direct await
• {} as HttpHeaders changed to createHttpHeaders()
• Removed redundant 0 as number cast
• deepEqual on primitives changed to strictEqual

[Copilot]

Pull request overview

This PR adds and extends Vitest coverage for @azure/core-rest-pipeline with the goal of reaching ~100% coverage, primarily by exercising previously untested branches across pipeline policies and internal utilities.

Changes:

• Adds new internal tests for tokenCycler, file, createPipelineFromOptions, Node policy factories, and user-agent helpers (Node + browser where applicable).
• Extends existing tests to cover additional branches in multiple pipeline policies (auth, tracing, request-id, NDJSON, user-agent platform).
• Introduces additional mocking to exercise error/edge paths (e.g., tracing client creation failure, non-recording spans, CAE challenge branches).

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk/core/core-rest-pipeline/test/public/tracingPolicy.spec.ts	Adds additional tracingPolicy branch tests (client creation failure, non-recording span, response header attribute, error processing paths, user-agent branch).
sdk/core/core-rest-pipeline/test/public/setClientRequestIdPolicy.spec.ts	Adds coverage for not overwriting an existing x-ms-client-request-id.
sdk/core/core-rest-pipeline/test/public/ndJsonPolicy.spec.ts	Adds pass-through coverage for non-array / non-string-body cases.
sdk/core/core-rest-pipeline/test/internal/tokenCycler.spec.ts	Adds new tests covering token refresh failure and retry loop behavior with fake timers.
sdk/core/core-rest-pipeline/test/internal/node/userAgentPolicy.spec.ts	Adds Node-only tests for User-Agent header overwrite behavior.
sdk/core/core-rest-pipeline/test/internal/node/userAgentPlatform.spec.ts	Improves mocking and expands runtime-detection branch coverage (Bun/Deno/Node/unknown).
sdk/core/core-rest-pipeline/test/internal/node/userAgent.spec.ts	Adds internal tests for user-agent string formatting/prefix handling and platform-data formatting edge cases.
sdk/core/core-rest-pipeline/test/internal/node/policyFactories.spec.ts	Adds tests for Node policy factory functions and proxy env parsing behavior.
sdk/core/core-rest-pipeline/test/internal/node/file.spec.ts	Adds Node tests for file utilities including stream behavior and raw content helpers.
sdk/core/core-rest-pipeline/test/internal/node/createPipelineFromOptions.spec.ts	Adds Node tests ensuring agent/tls policies are wired in via options.
sdk/core/core-rest-pipeline/test/internal/browser/file.spec.ts	Adds browser tests for file utilities including File constructor and stream factory behavior.
sdk/core/core-rest-pipeline/test/internal/browser/createPipelineFromOptions.spec.ts	Adds browser tests ensuring Node-only policies are excluded/ignored.
sdk/core/core-rest-pipeline/test/internal/bearerTokenAuthenticationPolicy.spec.ts	Refactors request creation helper and adds many new CAE/custom-challenge edge-path tests.
sdk/core/core-rest-pipeline/test/internal/auxiliaryAuthenticationHeaderPolicy.spec.ts	Refactors request creation helper and adds tests for empty/undefined credentials behavior.

[jeremymeng]

Looks good overall! I added some comments