feat(coverage): add cj/coverage-report command and F7 binding

Completes the coverage v1 user-facing path. cj/coverage-report is the interactive entry point:

1. Resolves the backend for the current project (honoring cj/coverage-backend from .dir-locals.el).
2. Prompts for a git-diff scope via completing-read (Working tree, Staged, Branch vs parent, Branch vs main).
3. Reads the cached simplecov report, intersects with the diff, renders records into a *Coverage Report* buffer.
4. If the report doesn't exist, prompts to run coverage first. With a prefix argument, re-runs regardless.

The report buffer uses cj/coverage-report-mode, a compilation-mode derivative. Uncovered-line entries are formatted as path:line: uncovered so the standard gnu compilation-error-regexp-alist picks them up for next-error navigation. That means M-g n, M-g p, and C-x backtick walk through uncovered lines from any buffer without switching focus.

F7 is bound to the command globally, matching the F-key layout ticket's design (F4 compile+run, F5 debug, F6 test, F7 coverage).

Added to init.el: (require 'coverage-core) + (require 'coverage-elisp).

Tests cover the pure scope-label helpers (label to symbol, symbol to label, roundtrip) plus a smoke test that exercises the full command with stubbed backend, stubbed completing-read, stubbed shell-command-to-string, and a prepared simplecov fixture.

Coverage v1 is now functionally complete: make coverage produces the report, F7 drives the interactive flow.

1 files changed, 90 insertions, 0 deletions

diff --git a/tests/test-coverage-core--command.el b/tests/test-coverage-core--command.el
new file mode 100644
index 00000000..d7b2c1cc
--- /dev/null
+++ b/tests/test-coverage-core--command.el
@@ -0,0 +1,90 @@
+;;; test-coverage-core--command.el --- Tests for cj/coverage-report and scope helpers -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for:
+;;   `cj/--coverage-scope-from-label' (pure label → symbol lookup)
+;;   `cj/--coverage-label-from-scope' (pure symbol → label lookup)
+;;   `cj/coverage-report' (one smoke test with stubbed git + prepared report)
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'coverage-core)
+
+;;; Scope label <-> symbol (pure lookups)
+
+(ert-deftest test-coverage-scope-from-label-known ()
+  "Normal: each registered label maps to its scope symbol."
+  (should (eq 'working-tree
+			  (cj/--coverage-scope-from-label
+			   "Working tree — all uncommitted changes")))
+  (should (eq 'staged
+			  (cj/--coverage-scope-from-label "Staged — about to commit")))
+  (should (eq 'branch-vs-parent
+			  (cj/--coverage-scope-from-label "Branch vs parent")))
+  (should (eq 'branch-vs-main
+			  (cj/--coverage-scope-from-label "Branch vs main"))))
+
+(ert-deftest test-coverage-scope-from-label-unknown ()
+  "Boundary: unknown label returns nil."
+  (should-not (cj/--coverage-scope-from-label "bogus label"))
+  (should-not (cj/--coverage-scope-from-label "")))
+
+(ert-deftest test-coverage-label-from-scope-roundtrip ()
+  "Normal: symbol → label → symbol is an identity."
+  (dolist (sym '(working-tree staged branch-vs-parent branch-vs-main))
+	(should (eq sym (cj/--coverage-scope-from-label
+					 (cj/--coverage-label-from-scope sym))))))
+
+;;; Smoke test for the interactive command
+
+(ert-deftest test-coverage-report-smoke-happy-path ()
+  "Smoke: cj/coverage-report with stubbed backend, scope, and git-diff
+populates the *Coverage Report* buffer with the expected summary and
+uncovered-line markers."
+  (let* ((tmp-root (make-temp-file "test-coverage-smoke-" t))
+		 (report-file (expand-file-name "simplecov.json" tmp-root))
+		 (simplecov (concat "{\"run\":{\"timestamp\":1,\"coverage\":"
+							"{\"modules/foo.el\":[null,1,0,1,0]}}}"))
+		 (diff-output (concat "diff --git a/modules/foo.el b/modules/foo.el\n"
+							  "--- a/modules/foo.el\n"
+							  "+++ b/modules/foo.el\n"
+							  "@@ -1,0 +2,4 @@\n"
+							  "+added 1\n+added 2\n+added 3\n+added 4\n"))
+		 (test-backend
+		  (list :name 'test-backend
+				:detect (lambda (_) t)
+				:run (lambda (cb) (funcall cb report-file))
+				:report-path (lambda (&rest _) report-file)))
+		 (cj/coverage-backends nil))
+	(unwind-protect
+		(progn
+		  (with-temp-file report-file (insert simplecov))
+		  (cj/coverage-register-backend test-backend)
+		  (cl-letf (((symbol-function 'completing-read)
+					 (lambda (&rest _) "Staged — about to commit"))
+					((symbol-function 'shell-command-to-string)
+					 (lambda (_) diff-output))
+					((symbol-function 'cj/--coverage-project-root)
+					 (lambda () tmp-root))
+					((symbol-function 'display-buffer) #'identity))
+			(call-interactively #'cj/coverage-report))
+		  (with-current-buffer "*Coverage Report*"
+			(let ((text (buffer-substring-no-properties (point-min) (point-max))))
+			  ;; Scope label appears
+			  (should (string-match-p "Staged" text))
+			  ;; Lines 2 and 4 hit, lines 3 and 5 uncovered (per simplecov)
+			  ;; Diff covers lines 2-5
+			  ;; So the summary should show 2 of 4 covered
+			  (should (string-match-p "2 of 4" text))
+			  ;; Uncovered line markers use compilation-friendly format
+			  (should (string-match-p "modules/foo\\.el:[35]: uncovered" text)))))
+	  (when (get-buffer "*Coverage Report*")
+		(kill-buffer "*Coverage Report*"))
+	  (delete-directory tmp-root t))))
+
+(provide 'test-coverage-core--command)
+;;; test-coverage-core--command.el ends here