Add detached current branch fixture

fixtures/detached/_git/HEAD

@@ -0,0 +1 @@
+2dbee47a8d4f8d39e1168fad951b703ee05614d6

fixtures/detached/_git/config

@@ -0,0 +1,13 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = false
+	logallrefupdates = true
+	ignorecase = true
+	precomposeunicode = true
+[remote "origin"]
+	url = /scan-git/
+	fetch = +refs/heads/*:refs/remotes/origin/*
+[branch "main"]
+	remote = origin
+	merge = refs/heads/main

fixtures/detached/_git/objects/2d/bee47a8d4f8d39e1168fad951b703ee05614d6

@@ -0,0 +1,3 @@
+x
��M
+�0F]��d�L~
+".<�x�i:Q�4c�o�7p�x�>�TKyv0&�z
�n�K����Ō
�4�K�H@	Y�������DG1�(>G�k�G�S���l��6���3\�����M��C��ڻh�&ka�Q�v���Z���a�P?*�H

fixtures/detached/_git/objects/info/packs

@@ -0,0 +1,2 @@
+P pack-43bc2b9ae5b7a56ab22e849c6c1dfaa00ba72ab1.pack
+

fixtures/detached/_git/refs/heads/main

@@ -0,0 +1 @@
+7b84f676f2fbea2a3c6d83924fa63059c7bdfbe2

fixtures/detached/data.json

@@ -0,0 +1 @@
+{}

test/helpers/fixture.ts

@@ -9,7 +9,7 @@ type LazyFixture = {
 };
 
 const fixturesPath = '../../fixtures/';
-const fixtureNames = ['base', 'cruft', 'no-remotes', 'upstream', 'clean', 'rev-index'];
+const fixtureNames = ['base', 'detached', 'cruft', 'no-remotes', 'upstream', 'clean', 'rev-index'];
 
 export const nullRepo: Repo = null as unknown as Repo;
 export const fixtures: Record<string, LazyFixture> = Object.create(null);
@@ -33,11 +33,17 @@ for (const name of fixtureNames) {
                 fs.promises.readdir = origReaddir;
             }
         },
-        data: JSON.parse(
-            fs.readFileSync(
-                fileURLToPath(new URL(fixturesPath + name + '/data.json', import.meta.url)),
-                'utf8'
-            )
-        )
+        get data() {
+            const value = JSON.parse(
+                fs.readFileSync(
+                    fileURLToPath(new URL(fixturesPath + name + '/data.json', import.meta.url)),
+                    'utf8'
+                )
+            );
+
+            Object.defineProperty(this, 'data', { value });
+
+            return value;
+        }
     };
 }