git-son: add tests

Add t5151-son.sh with nine test cases covering:

 - basic child repository creation
 - parent remote configuration in the child
 - .gitignore update in the parent
 - initial commit presence in the child
 - failure when the target directory already exists
 - --branch without --inherit is rejected cleanly
 - no leftover directory on validation failure
 - --inherit fetches parent history

Register the test in t/meson.build so the meson build system
discovers and runs it.

Assisted-by: Claude Opus 4.6
Signed-off-by: Evan Haque <evanhaque1@gmail.com>

Author: Evandabest

t/meson.build

@@ -591,6 +591,7 @@ integration_tests = [
   't5004-archive-corner-cases.sh',
   't5100-mailinfo.sh',
   't5150-request-pull.sh',
+  't5151-son.sh',
   't5200-update-server-info.sh',
   't5300-pack-object.sh',
   't5301-sliding-window.sh',

t/t5151-son.sh

@@ -0,0 +1,63 @@
+#!/bin/sh
+
+test_description='Test git son command.'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup parent repository' '
+	echo "parent content" >file.txt &&
+	git add file.txt &&
+	git commit -m "Initial parent commit"
+'
+
+test_expect_success 'son creates child repository' '
+	git son my-child &&
+	test -d my-child &&
+	test -d my-child/.git
+'
+
+test_expect_success 'son sets parent remote in child' '
+	(
+		cd my-child &&
+		git remote get-url parent
+	)
+'
+
+test_expect_success 'son adds child to parent .gitignore' '
+	grep "my-child/" .gitignore
+'
+
+test_expect_success 'son child has initial commit' '
+	(
+		cd my-child &&
+		test $(git log --oneline | wc -l) -eq 1
+	)
+'
+
+test_expect_success 'son fails if target already exists' '
+	test_must_fail git son my-child
+'
+
+test_expect_success 'son with --branch requires --inherit' '
+	test_must_fail git son --branch main branch-child
+'
+
+test_expect_success 'son with --branch leaves no directory on failure' '
+	! test -e branch-child
+'
+
+test_expect_success 'son with --inherit fetches parent history' '
+	git init --bare "$TRASH_DIRECTORY/parent.git" &&
+	git push "$TRASH_DIRECTORY/parent.git" main &&
+	git remote add origin "file://$TRASH_DIRECTORY/parent.git" &&
+	git son --inherit inherited-child &&
+	(
+		cd inherited-child &&
+		git log --oneline parent/main
+	)
+'
+
+test_done