go/mysql: stop TestStaticConfigHUP panicking inside EventuallyWithT

The previous deflake commit (e3cd779) ported the EventuallyWithT
callback verbatim from upstream's PR #19388, which uses `require.X(c,
...)`. That works on upstream's testify v1.11+, but this branch is
pinned to testify v1.9, where `CollectT.FailNow` is implemented as
`panic("Assertion failed")` and `EventuallyWithT` doesn't recover from
it — so the first failed poll crashes the goroutine. The job log
showed exactly that:

  panic: Assertion failed
  testify/assert.(*CollectT).FailNow ...
  EventuallyWithT.func1 ...
  FAIL  vitess.io/vitess/go/mysql

Replace `require.X(c, ...)` with `assert.X(c, ...)` (which just flags
the CollectT instead of panicking) and guard the `entries[0]` indexing
on `assert.NotEmpty`, otherwise a `nil[0]` slice access escapes the
same way.

Hoisted the polling loop into a `waitForReload` helper since both
hupTest and hupTestWithRotation now use the same body.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Arthur Schreiber <arthur@planetscale.com>
(cherry picked from commit 248182c)

Author: arthurschreiber

go/mysql/auth_server_static_test.go

@@ -160,10 +160,7 @@ func hupTest(t *testing.T, aStatic *AuthServerStatic, tmpFile *os.File, oldStr,
 	syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
 
 	// wait for signal handler
-	require.EventuallyWithT(t, func(c *assert.CollectT) {
-		require.Nil(c, aStatic.getEntries()[oldStr], "Should not have old %s after config reload", oldStr)
-		require.Equal(c, newStr, aStatic.getEntries()[newStr][0].Password, "%s's Password should be '%s'", newStr, newStr)
-	}, 30*time.Second, 10*time.Millisecond, "config should be reloaded with new file after rotation")
+	waitForReload(t, aStatic, oldStr, newStr)
 }
 
 func hupTestWithRotation(t *testing.T, aStatic *AuthServerStatic, tmpFile *os.File, oldStr, newStr string) {
@@ -172,9 +169,27 @@ func hupTestWithRotation(t *testing.T, aStatic *AuthServerStatic, tmpFile *os.Fi
 		t.Fatalf("couldn't overwrite temp file: %v", err)
 	}
 
+	waitForReload(t, aStatic, oldStr, newStr)
+}
+
+// waitForReload polls aStatic until the auth file reload has dropped oldStr
+// and installed newStr.
+//
+// We use `assert.X(c, ...)` (not `require.X`) inside the callback because
+// testify v1.9 on this branch implements `CollectT.FailNow` as
+// `panic("Assertion failed")`, and `EventuallyWithT` doesn't recover from
+// that — a failed poll would crash the test instead of being retried. We
+// also gate the `[0]` indexing on `NotEmpty` for the same reason: a panic
+// inside the callback (e.g. `nil[0]`) escapes the goroutine.
+func waitForReload(t *testing.T, aStatic *AuthServerStatic, oldStr, newStr string) {
+	t.Helper()
 	require.EventuallyWithT(t, func(c *assert.CollectT) {
-		require.Nil(c, aStatic.getEntries()[oldStr], "Should not have old %s after config reload", oldStr)
-		require.Equal(c, newStr, aStatic.getEntries()[newStr][0].Password, "%s's Password should be '%s'", newStr, newStr)
+		assert.Nil(c, aStatic.getEntries()[oldStr], "Should not have old %s after config reload", oldStr)
+		entries := aStatic.getEntries()[newStr]
+		if !assert.NotEmpty(c, entries, "Should have new %s entries after config reload", newStr) {
+			return
+		}
+		assert.Equal(c, newStr, entries[0].Password, "%s's Password should be '%s'", newStr, newStr)
 	}, 30*time.Second, 10*time.Millisecond, "config should be reloaded with new file after rotation")
 }