feat(dev-fkeys): add F6 test runner menu (Phase 2a)

I extended `dev-fkeys.el` with the F6 dispatcher half of the spec. F6 prompts via `completing-read` between two candidates: "All tests" delegates to `projectile-test-project`, and "Current file's tests" detects the buffer's language by extension, derives the runner command, and pipes through `compile' from the projectile root. C-F6 is the fast path straight to "Current file's tests".

Per-language coverage:

- Elisp source files map to `make test-name TEST=^test-<stem>-`. Elisp test files run with `make test-file FILE=<rel-path>` so a per-helper file like `test-foo--bar.el' runs only its own tests.
- Python source files map to `pytest tests/test_<stem>.py'. Python test files run with `pytest <rel-path>'.
- Go runs the package containing the file: `go test ./<rel-dir>'. Source and test files use the same command since Go test scope is per-package. Limit: this runs every `_test.go' in the package, not just the buffer's file. Phase 2b can refine via test-name discovery.
- TypeScript and JavaScript are detected but punted for v1. The runner-command builder returns nil and the orchestrator signals a user-error rather than guessing.

The F6 binding moved from the Phase 1 stopgap (`projectile-test-project') to `cj/f6-test-runner'. C-F6 is newly bound to `cj/f6-current-file-tests'. M-F6 stays unbound, reserved for Phase 2b's "Run a test..." menu entry.

TDD: 68 new tests across 7 files. Production code split into small testable internals (`cj/--f6-language-detect', `cj/--f6-buffer-is-test-file-p', `cj/--f6-source-stem', `cj/--f6-test-runner-cmd-for', `cj/--f6-current-file-tests-impl') plus two thin interactive wrappers. Smoke tests confirm bindings register on load.

I also updated the module commentary with the Phase 2b plan, the capture-then-filter approach for tree-sitter discovery, and a pointer to Emacs bug #79687. The bug is the predicate-syntax mismatch that breaks `:match' / `:equal' / `:pred' queries on Emacs 30.2 with libtree-sitter 0.26. The fix lives on Emacs master (commit b0143530), targets Emacs 31, and has not been backported to the emacs-30 branch as of today. Phase 2b will use queries without predicates and filter results in Elisp, sidestepping the issue. Mike Olson's `treesit-predicate-rewrite.el' applies the same idea to font-lock if you want it before Phase 2b lands.

1 files changed, 80 insertions, 0 deletions

diff --git a/tests/test-dev-fkeys--f6-language-detect.el b/tests/test-dev-fkeys--f6-language-detect.el
new file mode 100644
index 00000000..93dd6d8b
--- /dev/null
+++ b/tests/test-dev-fkeys--f6-language-detect.el
@@ -0,0 +1,80 @@
+;;; test-dev-fkeys--f6-language-detect.el --- Tests for cj/--f6-language-detect -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the language classifier used by the F6 test runner. Detection
+;; runs purely off the file extension. The classifier returns one of
+;; \\='elisp / \\='python / \\='go / \\='typescript / \\='javascript / \\='unknown.
+
+;;; Code:
+
+(require 'ert)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-f6-language-detect-elisp ()
+  "Normal: .el classifies as elisp."
+  (should (eq (cj/--f6-language-detect "foo.el") 'elisp)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-python ()
+  "Normal: .py classifies as python."
+  (should (eq (cj/--f6-language-detect "foo.py") 'python)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-go ()
+  "Normal: .go classifies as go."
+  (should (eq (cj/--f6-language-detect "foo.go") 'go)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-typescript ()
+  "Normal: .ts and .tsx classify as typescript."
+  (should (eq (cj/--f6-language-detect "foo.ts") 'typescript))
+  (should (eq (cj/--f6-language-detect "foo.tsx") 'typescript)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-javascript ()
+  "Normal: .js and .jsx classify as javascript."
+  (should (eq (cj/--f6-language-detect "foo.js") 'javascript))
+  (should (eq (cj/--f6-language-detect "foo.jsx") 'javascript)))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-f6-language-detect-with-directory-path ()
+  "Boundary: classifier ignores the path, looks only at extension."
+  (should (eq (cj/--f6-language-detect "/abs/path/to/foo.el") 'elisp))
+  (should (eq (cj/--f6-language-detect "rel/dir/foo.py") 'python)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-test-file-name ()
+  "Boundary: a filename that is itself a test file still classifies by extension.
+The test-file-vs-source distinction is a separate helper."
+  (should (eq (cj/--f6-language-detect "tests/test-foo.el") 'elisp))
+  (should (eq (cj/--f6-language-detect "tests/test_foo.py") 'python))
+  (should (eq (cj/--f6-language-detect "pkg/foo_test.go") 'go)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-uppercase-extension ()
+  "Boundary: extension match is case-insensitive (.PY, .EL, etc.)."
+  (should (eq (cj/--f6-language-detect "foo.EL") 'elisp))
+  (should (eq (cj/--f6-language-detect "foo.PY") 'python)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-no-extension ()
+  "Boundary: a filename with no extension classifies as unknown."
+  (should (eq (cj/--f6-language-detect "Makefile") 'unknown))
+  (should (eq (cj/--f6-language-detect "README") 'unknown)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-unsupported-extension ()
+  "Boundary: an extension we do not classify returns unknown."
+  (should (eq (cj/--f6-language-detect "foo.rs") 'unknown))
+  (should (eq (cj/--f6-language-detect "foo.rb") 'unknown))
+  (should (eq (cj/--f6-language-detect "foo.txt") 'unknown)))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-f6-language-detect-nil-filename ()
+  "Error: nil filename returns unknown without erroring (defensive against
+buffers that aren't backed by files)."
+  (should (eq (cj/--f6-language-detect nil) 'unknown)))
+
+(ert-deftest test-dev-fkeys-f6-language-detect-empty-filename ()
+  "Error: empty string returns unknown."
+  (should (eq (cj/--f6-language-detect "") 'unknown)))
+
+(provide 'test-dev-fkeys--f6-language-detect)
+;;; test-dev-fkeys--f6-language-detect.el ends here