tests: Add tests for (guix build json-utils).

* tests/json-utils.scm: New file.
* CODEOWNERS, etc/teams.scm, Makefile.am: Record tests/json-utils.scm.

Change-Id: Iab107b04d3234c3b26186c56aed96d00050bb425
Signed-off-by: Jelle Licht <jlicht@fsfe.org>

5 files changed, 270 insertions, 2 deletions

diff --git a/CODEOWNERS b/CODEOWNERS
index 774f0c3b89c..0c81de49cec 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -287,6 +287,7 @@ guix/build/json-utils\.scm                         @guix/javascript
 guix/build/node-build-system\.scm                  @guix/javascript
 guix/import/npm-binary\.scm                        @guix/javascript
 guix/scripts/import/npm-binary\.scm                @guix/javascript
+tests/json-utils\.scm                              @guix/javascript
 
 gnu/packages/julia(-.+|)\.scm$                     @guix/julia
 guix/build/julia-build-system\.scm                 @guix/julia
diff --git a/Makefile.am b/Makefile.am
index 5e1f252b9cc..061980e33ad 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -587,6 +587,7 @@ SCM_TESTS =					\
   tests/http-client.scm                         \
   tests/inferior.scm                            \
   tests/ipfs.scm                                \
+  tests/json-utils.scm                          \
   tests/ld-wrapper.scm                          \
   tests/lint.scm                                \
   tests/modules.scm                             \
diff --git a/etc/teams.scm b/etc/teams.scm
index 244f681ced1..c70ff61cb0e 100755
--- a/etc/teams.scm
+++ b/etc/teams.scm
@@ -884,7 +884,8 @@ and the maven-build-system."
                       "guix/build/json-utils.scm"
                       "guix/build/node-build-system.scm"
                       "guix/import/npm-binary.scm"
-                      "guix/scripts/import/npm-binary.scm")))
+                      "guix/scripts/import/npm-binary.scm"
+                      "tests/json-utils.scm")))
 
 (define-team julia
   (team 'julia
diff --git a/guix/build/json-utils.scm b/guix/build/json-utils.scm
index 67025a5b1ae..9d94fd85c4d 100644
--- a/guix/build/json-utils.scm
+++ b/guix/build/json-utils.scm
@@ -172,7 +172,7 @@ invalid field value provided, expected string or list of strings, got ~s~%")
                   (data (if (and field-missing? insert?)
                             (acons key '() data)
                             data)))
-             (if field-missing?
+             (if (and field-missing? (not insert?))
                  (if strict?
                      (raise (make-compound-condition
                              (condition (&modify-json-missing-key-error
diff --git a/tests/json-utils.scm b/tests/json-utils.scm
new file mode 100644
index 00000000000..3f0ad0b8a0d
--- /dev/null
+++ b/tests/json-utils.scm
@@ -0,0 +1,265 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2026 Nicolas Graves <ngraves@ngraves.fr>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix 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.
+;;;
+;;; GNU Guix 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 GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (test-json-utils)
+  #:use-module (guix build json-utils)
+  #:use-module (guix tests)
+  #:use-module (json)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-64))
+
+(define sample-json
+  '(("name" . "my-package")
+    ("version" . "1.0.0")
+    ("dependencies" . (("foo" . "^1.0.0")
+                       ("bar" . "^2.0.0")))
+    ("devDependencies" . (("baz" . "^3.0.0")
+                          ("qux" . "^4.0.0")))
+    ("scripts" . (("build" . "make build")
+                  ("test" . "make test")))))
+
+;; Many json-utils procedures use assoc-set! and assoc-remove! which
+;; mutate alist structure in place.  Use copy-tree to obtain a fresh
+;; deep copy for each test.
+(define (fresh-sample-json)
+  (copy-tree sample-json))
+
+(define (package.json)
+  "Sample package.json file as a JSON string."
+  (call-with-output-string
+   (cute scm->json sample-json <> #:pretty #t)))
+
+(define (with-atomic-file-replacement/mock _ proc)
+  "Mock for with-atomic-file-replacement: reads from package.json procedure,
+captures the written output as a string."
+  (call-with-input-string (package.json)
+    (lambda (in)
+      (call-with-output-string
+       (cute proc in <>)))))
+
+(define* (modify-json* #:rest all-arguments)
+  "Mock modify-json* with input from the package.json procedure."
+  (mock ((guix build utils) with-atomic-file-replacement
+         with-atomic-file-replacement/mock)
+    (json-string->scm (apply modify-json all-arguments))))
+
+(test-begin "json-utils")
+
+;;;
+;;; with-atomic-json-file-replacement
+;;;
+
+(test-equal "with-atomic-json-file-replacement, modify top-level field"
+  "2.0.0"
+  (assoc-ref
+   (modify-json* (cut assoc-set! <> "version" "2.0.0"))
+   "version"))
+
+;;;
+;;; delete-json-fields
+;;;
+
+(test-assert "delete-json-fields, single top-level field"
+  (let ((result ((delete-json-fields '("version")) (fresh-sample-json))))
+    (and (not (assoc-ref result "version"))
+         (assoc-ref result "name"))))
+
+(test-assert "delete-json-fields, multiple top-level fields"
+  (let ((result ((delete-json-fields '("version" "name")) (fresh-sample-json))))
+    (and (not (assoc-ref result "version"))
+         (not (assoc-ref result "name"))
+         (assoc-ref result "dependencies"))))
+
+(test-assert "delete-json-fields, nested field with dot syntax"
+  (let ((result ((delete-json-fields '("dependencies.foo")) (fresh-sample-json))))
+    (and (not (assoc-ref (assoc-ref result "dependencies") "foo"))
+         (assoc-ref (assoc-ref result "dependencies") "bar"))))
+
+(test-assert "delete-json-fields, nested field with list syntax"
+  (let ((result ((delete-json-fields '(("dependencies" "bar")))
+                 (fresh-sample-json))))
+    (and (not (assoc-ref (assoc-ref result "dependencies") "bar"))
+         (assoc-ref (assoc-ref result "dependencies") "foo"))))
+
+(test-assert "delete-json-fields, missing field with strict? #f"
+  (let ((result ((delete-json-fields '("nonexistent") #:strict? #f)
+                 (fresh-sample-json))))
+    (assoc-ref result "name")))
+
+(test-error "delete-json-fields, missing field with strict? #t raises error"
+  &modify-json-missing-key-error
+  ((delete-json-fields '("nonexistent") #:strict? #t) (fresh-sample-json)))
+
+(test-assert "delete-json-fields, missing nested field with strict? #f"
+  (let ((result ((delete-json-fields '("dependencies.nonexistent")
+                                     #:strict? #f)
+                 (fresh-sample-json))))
+    (assoc-ref (assoc-ref result "dependencies") "foo")))
+
+;;;
+;;; replace-json-fields
+;;;
+
+(test-equal "replace-json-fields, single top-level field"
+  "new-name"
+  (assoc-ref
+   ((replace-json-fields '(("name" . "new-name"))) (fresh-sample-json))
+   "name"))
+
+(test-equal "replace-json-fields, nested field with dot syntax"
+  "^5.0.0"
+  (assoc-ref
+   (assoc-ref
+    ((replace-json-fields '(("dependencies.foo" . "^5.0.0")))
+     (fresh-sample-json))
+    "dependencies")
+   "foo"))
+
+(test-equal "replace-json-fields, nested field with list syntax"
+  "^6.0.0"
+  (assoc-ref
+   (assoc-ref
+    ((replace-json-fields '((("dependencies" "bar") . "^6.0.0")))
+     (fresh-sample-json))
+    "dependencies")
+   "bar"))
+
+(test-equal "replace-json-fields, multiple replacements"
+  '("new-name" . "2.0.0")
+  (let ((result ((replace-json-fields
+                  '(("name" . "new-name")
+                    ("version" . "2.0.0")))
+                 (fresh-sample-json))))
+    (cons (assoc-ref result "name")
+          (assoc-ref result "version"))))
+
+(test-error "replace-json-fields, missing field with strict? #t raises error"
+  &modify-json-missing-key-error
+  ((replace-json-fields '(("nonexistent" . "value")) #:strict? #t)
+   (fresh-sample-json)))
+
+(test-assert "replace-json-fields, missing field with strict? #f"
+  (let ((result ((replace-json-fields '(("nonexistent" . "value"))
+                                      #:strict? #f)
+                 (fresh-sample-json))))
+    (equal? (assoc-ref result "name") "my-package")))
+
+;;;
+;;; modify-json-fields
+;;;
+
+(test-equal "modify-json-fields, custom modifier on top-level field"
+  "MY-PACKAGE"
+  (assoc-ref
+   ((modify-json-fields '("name")
+      (lambda (field data key)
+        (assoc-set! data key (string-upcase (assoc-ref data key)))))
+    (fresh-sample-json))
+   "name"))
+
+(test-equal "modify-json-fields, custom modifier on nested field"
+  "^1.0.0-patched"
+  (assoc-ref
+   (assoc-ref
+    ((modify-json-fields '("dependencies.foo")
+       (lambda (field data key)
+         (assoc-set! data key
+                     (string-append (assoc-ref data key) "-patched"))))
+     (fresh-sample-json))
+    "dependencies")
+   "foo"))
+
+(test-assert "modify-json-fields, insert? creates missing field"
+  (let ((result ((modify-json-fields '("newField")
+                   (lambda (field data key)
+                     (assoc-set! data key "inserted"))
+                   #:insert? #t)
+                 (fresh-sample-json))))
+    (equal? (assoc-ref result "newField") "inserted")))
+
+(test-assert "modify-json-fields, insert? creates nested missing fields"
+  (let ((result ((modify-json-fields '("newSection.newKey")
+                   (lambda (field data key)
+                     (assoc-set! data key "deep-insert"))
+                   #:insert? #t)
+                 (fresh-sample-json))))
+    (equal? (assoc-ref (assoc-ref result "newSection") "newKey")
+            "deep-insert")))
+
+(test-assert "modify-json-fields, field-path-mapper"
+  (let ((result ((modify-json-fields '(("name" . "REPLACED"))
+                   (lambda (field data key)
+                     (assoc-set! data key (cdr field)))
+                   #:field-path-mapper car)
+                 (fresh-sample-json))))
+    (equal? (assoc-ref result "name") "REPLACED")))
+
+(test-error "modify-json-fields, invalid field-path raises error"
+  &modify-json-invalid-field-value-error
+  ((modify-json-fields '(42) (lambda (field data key) data))
+   (fresh-sample-json)))
+
+;;;
+;;; modify-json (deprecated wrapper)
+;;;
+
+(test-equal "modify-json, single modification"
+  "modified"
+  (assoc-ref
+   (modify-json* (cut assoc-set! <> "name" "modified"))
+   "name"))
+
+(test-equal "modify-json, chained modifications"
+  '("chain-name" . "3.0.0")
+  (let ((result (modify-json*
+                 (cut assoc-set! <> "name" "chain-name")
+                 (cut assoc-set! <> "version" "3.0.0"))))
+    (cons (assoc-ref result "name")
+          (assoc-ref result "version"))))
+
+;;;
+;;; Integration: delete-json-fields and replace-json-fields with modify-json
+;;;
+
+(test-equal "modify-json + delete-json-fields integration"
+  #f
+  (assoc-ref
+   (modify-json* (delete-json-fields '("devDependencies")))
+   "devDependencies"))
+
+(test-equal "modify-json + replace-json-fields integration"
+  "^9.0.0"
+  (assoc-ref
+   (assoc-ref
+    (modify-json* (replace-json-fields '(("dependencies.foo" . "^9.0.0"))))
+    "dependencies")
+   "foo"))
+
+(test-equal "modify-json + chained delete and replace integration"
+  '(#f . "replaced-name")
+  (let ((result (modify-json*
+                  (delete-json-fields '("devDependencies"))
+                  (replace-json-fields '(("name" . "replaced-name"))))))
+    (cons (assoc-ref result "devDependencies")
+          (assoc-ref result "name"))))
+
+(test-end "json-utils")
+
+;; Local Variables:
+;; eval: (put 'modify-json-fields 'scheme-indent-function 1)
+;; End: