docs(test): document status code flushing behavior in CreateTestContext

[RubenPari]

Summary

CreateTestContext does not flush the response at the end of a handler, unlike Engine.ServeHTTP. This caused confusion (issue #3443) when ctx.Status(http.StatusCreated) was not observable in the httptest.ResponseRecorder without calling ctx.Writer.WriteHeaderNow().

Root cause

In a real server, http.Server flushes the response after the handler returns. CreateTestContext calls the handler directly without the http.Server infrastructure, so the status code set by Context.Status remains buffered in the gin responseWriter and is never written to the underlying http.ResponseWriter.

Changes

• Documented the buffering behavior in CreateTestContext and CreateTestContextOnly doc comments, explaining that c.Writer.WriteHeaderNow() must be called to observe the status code in the ResponseWriter after a handler that only calls Context.Status.
• Added TestCreateTestContextStatusRequiresFlush — a regression test that verifies:
  • c.Status(201) sets the buffered status (c.Writer.Status() == 201)
  • The httptest.ResponseRecorder still shows 200 (not yet flushed)
  • After c.Writer.WriteHeaderNow(), the recorder observes 201

No behavior change — documentation and test only.

Fixes #3443

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.65%. Comparing base (3b08cd7) to head (b045f4c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4801   +/-   ##
=======================================
  Coverage   98.65%   98.65%           
=======================================
  Files          48       48           
  Lines        3190     3190           
=======================================
  Hits         3147     3147           
  Misses         43       43           

Flag	Coverage Δ
--ldflags="-checklinkname=0" -tags sonic	98.64% <ø> (ø)
-tags go_json	98.57% <ø> (ø)
-tags nomsgpack	98.63% <ø> (ø)
go-1.26	98.33% <ø> (ø)
go-1.27	98.67% <ø> (ø)
macos-latest	98.65% <ø> (ø)
ubuntu-latest	98.65% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.