test: cover the coverage-summary tooling

scripts/coverage-summary.el carries real JSON parsing and report-formatting logic, but make coverage instruments only duet.el, so the tool itself had no tests. This adds them, mirroring the pattern from the other package's suite: synthetic SimpleCov reports written to temp files, so the tests are pure and need no prior coverage run.

The cases cover the normal percentage path, a fully covered file, a file with no executable lines, a multi-key union, basename-versus-path key matching, a tracked source absent from the report counting as 0%, missing and malformed JSON erroring as a user-error, and the formatted summary text.

There is no new target. The test file requires the script and runs under make test like every other suite, holding the tooling to the same bar as the package.

1 files changed, 172 insertions, 0 deletions

diff --git a/tests/test-duet-coverage-summary.el b/tests/test-duet-coverage-summary.el
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+++ b/tests/test-duet-coverage-summary.el
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+;;; test-duet-coverage-summary.el --- Tests for the coverage summary script -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Unit tests for scripts/coverage-summary.el — the batch helper behind
+;; `make coverage-summary'.  Drives the SimpleCov parsers, the per-file record
+;; builder, basename/path key matching, and the formatted text on synthetic
+;; reports written to temp files (no committed fixtures, no prior coverage
+;; run).  Covers the normal percentage path, boundary cases (fully covered, no
+;; executable lines, multi-key union, basename match), and error cases (missing
+;; file, malformed JSON, a tracked source absent from the report as 0%).
+
+;;; Code:
+
+(require 'ert)
+(load (expand-file-name "../scripts/coverage-summary.el"
+                        (file-name-directory (or load-file-name buffer-file-name)))
+      nil t)
+
+(defconst test-duet-cov-root "/tmp/duet-cov-test/"
+  "Synthetic project root used to anchor source-file paths in fixtures.")
+
+(defun test-duet-cov--write (json)
+  "Write JSON to a temp file and return its path."
+  (let ((f (make-temp-file "duet-cov" nil ".json")))
+    (with-temp-file f (insert json))
+    f))
+
+(defun test-duet-cov--report (hits-array)
+  "Write a SimpleCov report mapping duet.el under the test root to HITS-ARRAY.
+HITS-ARRAY is a JSON array literal string such as \"[null, 1, 0]\"."
+  (test-duet-cov--write
+   (format "{\"undercover\": {\"coverage\": {\"%sduet.el\": %s}}}"
+           test-duet-cov-root hits-array)))
+
+(defmacro test-duet-cov--with (json-or-path varname &rest body)
+  "Bind VARNAME to a report path from JSON-OR-PATH, run BODY, then delete it."
+  (declare (indent 2))
+  `(let ((,varname ,json-or-path))
+     (unwind-protect (progn ,@body)
+       (when (file-exists-p ,varname) (delete-file ,varname)))))
+
+;;; --- Parsers ---
+
+(ert-deftest test-duet-coverage-parse-counts-only-hit-lines ()
+  "`parse-simplecov' records only lines whose hit count is greater than zero."
+  (test-duet-cov--with (test-duet-cov--report "[null, 1, 0, 3, null, 0]") f
+    (let ((tbl (duet-coverage--parse-simplecov f))
+          (key (expand-file-name "duet.el" test-duet-cov-root)))
+      (should (= 2 (duet-coverage--line-count tbl key))))))
+
+(ert-deftest test-duet-coverage-executable-counts-all-numeric-lines ()
+  "`executable-lines' records every numeric entry, hit or not."
+  (test-duet-cov--with (test-duet-cov--report "[null, 1, 0, 3, null, 0]") f
+    (let ((tbl (duet-coverage--executable-lines f))
+          (key (expand-file-name "duet.el" test-duet-cov-root)))
+      (should (= 4 (duet-coverage--line-count tbl key))))))
+
+(ert-deftest test-duet-coverage-parse-unions-across-test-keys ()
+  "Coverage under multiple top-level keys is unioned (undercover :merge-report)."
+  (test-duet-cov--with
+      (test-duet-cov--write
+       (format (concat "{\"a\": {\"coverage\": {\"%sduet.el\": [1, 0, null]}},"
+                       " \"b\": {\"coverage\": {\"%sduet.el\": [0, 1, null]}}}")
+               test-duet-cov-root test-duet-cov-root))
+      f
+    (let ((tbl (duet-coverage--parse-simplecov f))
+          (key (expand-file-name "duet.el" test-duet-cov-root)))
+      (should (= 2 (duet-coverage--line-count tbl key))))))
+
+;;; --- Records ---
+
+(ert-deftest test-duet-coverage-record-normal-percentage ()
+  "A half-covered file reports covered/total and a 50% figure."
+  (test-duet-cov--with (test-duet-cov--report "[null, 1, 0, 3, null, 0]") f
+    (let ((r (car (duet-coverage--records f '("duet.el") test-duet-cov-root))))
+      (should (plist-get r :present))
+      (should (= 2 (plist-get r :covered)))
+      (should (= 4 (plist-get r :total)))
+      (should (< 49.9 (plist-get r :percent) 50.1)))))
+
+(ert-deftest test-duet-coverage-record-fully-covered-is-100 ()
+  "Every executable line hit reports 100%."
+  (test-duet-cov--with (test-duet-cov--report "[1, 2, 3]") f
+    (let ((r (car (duet-coverage--records f '("duet.el") test-duet-cov-root))))
+      (should (= 3 (plist-get r :covered)))
+      (should (= 3 (plist-get r :total)))
+      (should (< 99.9 (plist-get r :percent) 100.1)))))
+
+(ert-deftest test-duet-coverage-record-no-executable-lines-is-100 ()
+  "A present file with no executable lines is 100% — nothing left uncovered."
+  (test-duet-cov--with (test-duet-cov--report "[null, null]") f
+    (let ((r (car (duet-coverage--records f '("duet.el") test-duet-cov-root))))
+      (should (plist-get r :present))
+      (should (= 0 (plist-get r :total)))
+      (should (< 99.9 (plist-get r :percent) 100.1)))))
+
+(ert-deftest test-duet-coverage-record-missing-source-counts-as-zero ()
+  "A tracked source absent from the report is flagged missing and counts as 0%."
+  (test-duet-cov--with
+      (test-duet-cov--write
+       (format "{\"u\": {\"coverage\": {\"%sother.el\": [1, 2]}}}"
+               test-duet-cov-root))
+      f
+    (let ((r (car (duet-coverage--records f '("duet.el") test-duet-cov-root))))
+      (should-not (plist-get r :present))
+      (should (= 0 (plist-get r :covered)))
+      (should (= 0.0 (plist-get r :percent))))))
+
+(ert-deftest test-duet-coverage-record-matches-by-basename ()
+  "A report whose path is written differently still resolves by basename."
+  (test-duet-cov--with
+      (test-duet-cov--write "{\"u\": {\"coverage\": {\"duet.el\": [1, 0, 1]}}}")
+      f
+    (let ((r (car (duet-coverage--records f '("duet.el") test-duet-cov-root))))
+      (should (plist-get r :present))
+      (should (= 2 (plist-get r :covered)))
+      (should (= 3 (plist-get r :total))))))
+
+;;; --- Error handling ---
+
+(ert-deftest test-duet-coverage-missing-report-errors ()
+  "Parsing a nonexistent report signals a user-error."
+  (should-error (duet-coverage--parse-simplecov "/nonexistent/duet-cov.json")
+                :type 'user-error))
+
+(ert-deftest test-duet-coverage-malformed-json-errors ()
+  "Malformed JSON signals a user-error rather than a raw json error."
+  (test-duet-cov--with (test-duet-cov--write "{ this is not json") f
+    (should-error (duet-coverage--parse-simplecov f) :type 'user-error)))
+
+;;; --- Formatted text ---
+
+(ert-deftest test-duet-coverage-summary-text-reports-both-numbers ()
+  "The summary names the file, a line-coverage figure, and source coverage."
+  (test-duet-cov--with (test-duet-cov--report "[null, 1, 0, 3, null, 0]") f
+    (let ((txt (duet-coverage-summary-text f '("duet.el") test-duet-cov-root)))
+      (should (string-match-p "duet\\.el" txt))
+      (should (string-match-p "Line coverage" txt))
+      (should (string-match-p "Source coverage" txt))
+      (should (string-match-p "50\\.0%" txt)))))
+
+(ert-deftest test-duet-coverage-summary-text-lists-missing-source ()
+  "The summary's missing section names a tracked source absent from the report."
+  (test-duet-cov--with
+      (test-duet-cov--write
+       (format "{\"u\": {\"coverage\": {\"%sother.el\": [1, 2]}}}"
+               test-duet-cov-root))
+      f
+    (let ((txt (duet-coverage-summary-text f '("duet.el") test-duet-cov-root)))
+      (should (string-match-p "Not in coverage report" txt))
+      (should (string-match-p "duet\\.el" txt)))))
+
+(provide 'test-duet-coverage-summary)
+;;; test-duet-coverage-summary.el ends here