Use testify in the internal tests

[crhntr]

Converts the tests under internal/ from hand-rolled if got != want { t.Errorf(...) } checks to testify, package by package, and makes the ones that were hard to follow easier to read. Only _test.go files change: no non-test file, nothing under cmd/, and no testdata or snapshot archive.

Conversion

• t.Errorf became assert, and t.Fatal became require, so a check that used to continue still continues and one that stopped still stops.
• No assertion was removed or loosened. Exact error-string checks stay exact, expected values come first, and failure messages still name the input.
• Loops and sequential blocks that checked several unrelated things became named subtests; repeated setup moved into small helpers.
• The snapshot harnesses keep their -update behavior and file layout.
• configurations_test.go, header_test.go and other files that already used testify consistently were left alone.

TestTypeFormatter is now eight one-behavior subtests, each with its own formatter, covering the nil and output package, the numeric suffix, the memoized name, skipping declared names, same-named packages, the sorted import declaration, and the JSON key order.

Coverage and mutation testing

For every internal package I compared per-function go tool cover -func output before and after. It is identical for all eleven, so no function lost coverage. Gremlins gives the same killed, lived and not-covered counts as before the change:

Package	Killed	Lived	Not covered
muxt	352	0	17
generate	135	0	3
cli	157	4	0
analysis	103	0	4
astgen	46	0	0
load	59	8	1
header	12	0	0
fakeserver	9	0	0
mutation	148	13	6

mutation was run on its main source files only, because each mutant costs a full test suite. The full suite passes with -race -shuffle=on.

Tests that checked less than they looked like

Fixed as part of the conversion:

• The check that a TypeFormatter keeps the name it assigned could not tell memoization from recomputation; it now also runs after the declared names change.
• TestReportTrims asserted nothing; it now asserts that it does not panic.
• TestWalkActionsOrder and TestWalkActionsNarrowsDot joined slices into strings before comparing; they now compare the slices.
• TestNearestString skipped its suggestion check when nothing matched.
• TestDecisionRefusesWhatItCannotModel made an unchecked type assertion that would panic.
• TestImports passed got and want the wrong way round.

Left as they were, because removing a case would change what is tested:

• TestVersionCommand never checks its error when the CLI version is known.
• TestTemplateName_ByPathThenMethod repeats one case verbatim, and one case in that file has a no-op assertion.
• Two subtests in TestNewTemplateName share a name.

🤖 Generated with Claude Code