diff --git a/packages/steiger-plugin-fsd/src/_lib/find-all-recursively.ts b/packages/steiger-plugin-fsd/src/_lib/find-all-recursively.ts
index 6701b7c..77ae9e8 100644
--- a/packages/steiger-plugin-fsd/src/_lib/find-all-recursively.ts
+++ b/packages/steiger-plugin-fsd/src/_lib/find-all-recursively.ts
@@ -1,7 +1,7 @@
 import { basename } from 'node:path'
 import type { Folder, File } from '@feature-sliced/filesystem'
 
-import { parseIntoFsdRoot as parseIntoFolder } from './prepare-test.js'
+import { joinFromRoot, parseIntoFsdRoot as parseIntoFolder } from './prepare-test.js'
 
 /** Recursively walk through a folder and return all entries that satisfy the predicate in a flat array. */
 export function findAllRecursively(folder: Folder, predicate: (entry: Folder | File) => boolean): Array<Folder | File> {
@@ -54,9 +54,9 @@ if (import.meta.vitest) {
     )
 
     expect(result.map((entry) => entry.path)).toEqual([
-      '/folder1/directory1',
-      '/folder2/folder3/directory2',
-      '/directory3',
+      joinFromRoot('folder1', 'directory1'),
+      joinFromRoot('folder2', 'folder3', 'directory2'),
+      joinFromRoot('directory3'),
     ])
   })
 }
diff --git a/packages/steiger-plugin-fsd/src/_lib/group-slices.ts b/packages/steiger-plugin-fsd/src/_lib/group-slices.ts
index 66e23aa..e8c4a67 100644
--- a/packages/steiger-plugin-fsd/src/_lib/group-slices.ts
+++ b/packages/steiger-plugin-fsd/src/_lib/group-slices.ts
@@ -1,4 +1,4 @@
-import { sep } from 'node:path'
+import { sep, join } from 'node:path'
 
 export function groupSlices(sliceNames: Array<string>): Record<string, Array<string>> {
   const groups: Record<string, Array<string>> = {}
@@ -20,8 +20,8 @@ export function groupSlices(sliceNames: Array<string>): Record<string, Array<str
 if (import.meta.vitest) {
   const { test, expect } = import.meta.vitest
   test('groupSlices', () => {
-    expect(groupSlices(['a/b/c', 'a/b/d', 'a/e', 'f', 'g'])).toEqual({
-      'a/b': ['c', 'd'],
+    expect(groupSlices([join('a', 'b', 'c'), join('a', 'b', 'd'), join('a', 'e'), 'f', 'g'])).toEqual({
+      [join('a', 'b')]: ['c', 'd'],
       a: ['e'],
       '': ['f', 'g'],
     })
diff --git a/packages/steiger-plugin-fsd/src/_lib/prepare-test.ts b/packages/steiger-plugin-fsd/src/_lib/prepare-test.ts
index 7daf1b4..0f674dd 100644
--- a/packages/steiger-plugin-fsd/src/_lib/prepare-test.ts
+++ b/packages/steiger-plugin-fsd/src/_lib/prepare-test.ts
@@ -85,39 +85,39 @@ if (import.meta.vitest) {
 
     expect(root).toEqual({
       type: 'folder',
-      path: '/',
+      path: joinFromRoot(),
       children: [
         {
           type: 'folder',
-          path: '/entities',
+          path: joinFromRoot('entities'),
           children: [
             {
               type: 'folder',
-              path: '/entities/users',
+              path: joinFromRoot('entities', 'users'),
               children: [
                 {
                   type: 'folder',
-                  path: '/entities/users/ui',
+                  path: joinFromRoot('entities', 'users', 'ui'),
                   children: [],
                 },
                 {
                   type: 'file',
-                  path: '/entities/users/index.ts',
+                  path: joinFromRoot('entities', 'users', 'index.ts'),
                 },
               ],
             },
             {
               type: 'folder',
-              path: '/entities/posts',
+              path: joinFromRoot('entities', 'posts'),
               children: [
                 {
                   type: 'folder',
-                  path: '/entities/posts/ui',
+                  path: joinFromRoot('entities', 'posts', 'ui'),
                   children: [],
                 },
                 {
                   type: 'file',
-                  path: '/entities/posts/index.ts',
+                  path: joinFromRoot('entities', 'posts', 'index.ts'),
                 },
               ],
             },
@@ -125,19 +125,19 @@ if (import.meta.vitest) {
         },
         {
           type: 'folder',
-          path: '/shared',
+          path: joinFromRoot('shared'),
           children: [
             {
               type: 'folder',
-              path: '/shared/ui',
+              path: joinFromRoot('shared', 'ui'),
               children: [
                 {
                   type: 'file',
-                  path: '/shared/ui/index.ts',
+                  path: joinFromRoot('shared', 'ui', 'index.ts'),
                 },
                 {
                   type: 'file',
-                  path: '/shared/ui/Button.tsx',
+                  path: joinFromRoot('shared', 'ui', 'Button.tsx'),
                 },
               ],
             },
diff --git a/packages/steiger-plugin-fsd/src/insignificant-slice/index.spec.ts b/packages/steiger-plugin-fsd/src/insignificant-slice/index.spec.ts
index d00a8e1..64af733 100644
--- a/packages/steiger-plugin-fsd/src/insignificant-slice/index.spec.ts
+++ b/packages/steiger-plugin-fsd/src/insignificant-slice/index.spec.ts
@@ -1,4 +1,5 @@
 import { expect, it, vi } from 'vitest'
+import { join } from 'node:path'
 
 import { compareMessages, parseIntoFsdRoot } from '../_lib/prepare-test.js'
 import insignificantSlice from './index.js'
@@ -122,10 +123,10 @@ it('reports errors on a project with insignificant slices', async () => {
 
   expect((await insignificantSlice.check(root)).diagnostics.sort(compareMessages)).toEqual([
     {
-      message: 'Slice "entities/product" has no references. Consider removing it.',
+      message: `Slice "${join('entities', 'product')}" has no references. Consider removing it.`,
     },
     {
-      message: 'Slice "entities/user" has only one reference in slice "pages/editor". Consider merging them.',
+      message: `Slice "${join('entities', 'user')}" has only one reference in slice "${join('pages', 'editor')}". Consider merging them.`,
     },
   ])
 })
diff --git a/packages/steiger-plugin-fsd/src/no-reserved-folder-names/index.spec.ts b/packages/steiger-plugin-fsd/src/no-reserved-folder-names/index.spec.ts
index f1d4038..776d7fd 100644
--- a/packages/steiger-plugin-fsd/src/no-reserved-folder-names/index.spec.ts
+++ b/packages/steiger-plugin-fsd/src/no-reserved-folder-names/index.spec.ts
@@ -1,4 +1,5 @@
 import { expect, it } from 'vitest'
+import { join } from 'node:path'
 
 import noReservedFolderNames from './index.js'
 import { parseIntoFsdRoot } from '../_lib/prepare-test.js'
@@ -43,5 +44,7 @@ it('reports errors on a project with subfolders in segments that use reserved na
   `)
 
   const diagnostics = noReservedFolderNames.check(root).diagnostics
-  expect(diagnostics).toEqual([{ message: 'Folder name "lib" in "shared/ui" is reserved for segment names' }])
+  expect(diagnostics).toEqual([
+    { message: `Folder name "lib" in "${join('shared', 'ui')}" is reserved for segment names` },
+  ])
 })
diff --git a/packages/steiger-plugin-fsd/src/no-segmentless-slices/index.spec.ts b/packages/steiger-plugin-fsd/src/no-segmentless-slices/index.spec.ts
index 5c7a27e..306d640 100644
--- a/packages/steiger-plugin-fsd/src/no-segmentless-slices/index.spec.ts
+++ b/packages/steiger-plugin-fsd/src/no-segmentless-slices/index.spec.ts
@@ -1,4 +1,5 @@
 import { expect, it } from 'vitest'
+import { join } from 'node:path'
 
 import noSegmentlessSlices from './index.js'
 import { parseIntoFsdRoot } from '../_lib/prepare-test.js'
@@ -53,6 +54,6 @@ it('reports errors on a project where some slices have no segments', () => {
   const diagnostics = noSegmentlessSlices.check(root).diagnostics
   expect(diagnostics).toEqual([
     { message: 'Slice "user" on layer "entities" has no segments' },
-    { message: 'Slice "settings/profile" on layer "pages" has no segments' },
+    { message: `Slice "${join('settings', 'profile')}" on layer "pages" has no segments` },
   ])
 })
diff --git a/packages/steiger-plugin-fsd/src/public-api/index.spec.ts b/packages/steiger-plugin-fsd/src/public-api/index.spec.ts
index be55878..981e72c 100644
--- a/packages/steiger-plugin-fsd/src/public-api/index.spec.ts
+++ b/packages/steiger-plugin-fsd/src/public-api/index.spec.ts
@@ -1,7 +1,7 @@
 import { expect, it } from 'vitest'
 
 import publicApi from './index.js'
-import { compareMessages, parseIntoFsdRoot } from '../_lib/prepare-test.js'
+import { compareMessages, joinFromRoot, parseIntoFsdRoot } from '../_lib/prepare-test.js'
 
 it('reports no errors on a project with all the required public APIs', () => {
   const root = parseIntoFsdRoot(`
@@ -54,7 +54,7 @@ it('reports errors on slices that are missing a public API', () => {
       fixes: [
         {
           type: 'create-file',
-          path: '/entities/posts/index.ts',
+          path: joinFromRoot('entities', 'posts', 'index.ts'),
           content: '',
         },
       ],
@@ -64,7 +64,7 @@ it('reports errors on slices that are missing a public API', () => {
       fixes: [
         {
           type: 'create-file',
-          path: '/pages/editor/index.ts',
+          path: joinFromRoot('pages', 'editor', 'index.ts'),
           content: '',
         },
       ],
@@ -103,7 +103,7 @@ it('reports errors on segments that are missing a public API', () => {
       fixes: [
         {
           type: 'create-file',
-          path: '/shared/ui/index.ts',
+          path: joinFromRoot('shared', 'ui', 'index.ts'),
           content: '',
         },
       ],