diff --git a/src/domain/FileSystem/Change.ts b/src/domain/FileSystem/Change.ts
index 31ec0ddf..cd21cadc 100644
--- a/src/domain/FileSystem/Change.ts
+++ b/src/domain/FileSystem/Change.ts
@@ -5,7 +5,7 @@ import { LocalFileInfo } from './LocalFileInfo';
 import { RemoteFileInfo, RemoteNodeInfo } from './RemoteNodeInfo';
 
 export type RemoteChangeType =
-  | tagged.Tagged<'noChange'>
+  | tagged.Tagged<'noChange'> // fixme: seems to be unused - remove
   | tagged.Tagged<'updated', number>
   | tagged.Tagged<'removed'>
   | tagged.Tagged<'added', number>;
@@ -13,7 +13,7 @@ export type RemoteChangeType =
 export const remoteChangeType = tagged.build<RemoteChangeType>();
 
 export type LocalChangeType =
-  | tagged.Tagged<'noChange'>
+  | tagged.Tagged<'noChange'> // fixme: seems to be unused - remove
   | tagged.Tagged<'updated'>
   | tagged.Tagged<'removed'>
   | tagged.Tagged<'added'>;
@@ -73,7 +73,7 @@ export const getRemoteChanges = (
     array.map(({ type, path, version }) => ({
       type,
       path,
-      change: remoteChangeType.updated(version),
+      change: remoteChangeType.updated(version), // fixme: use latest version here
     })),
   );
   return pipe(
diff --git a/src/domain/FileSystem/Conflict.ts b/src/domain/FileSystem/Conflict.ts
index 94b9b3ef..f9c36a34 100644
--- a/src/domain/FileSystem/Conflict.ts
+++ b/src/domain/FileSystem/Conflict.ts
@@ -22,6 +22,7 @@ export const getConflicts = (
         remote,
         array.findFirst((changeRemote) => eqFsNode.equals(changeLocal, changeRemote)),
         option.map(({ change }) => change),
+        // fixme: don't do this: instead, replace array.intersection with a groupBy(getPath)
         option.getOrElseW(() => remoteChangeType.noChange()),
       ),
     })),
diff --git a/src/domain/FileSystem/HashInfo.ts b/src/domain/FileSystem/HashInfo.ts
index 27816c9a..63aadf55 100644
--- a/src/domain/FileSystem/HashInfo.ts
+++ b/src/domain/FileSystem/HashInfo.ts
@@ -15,6 +15,7 @@ export const hashInfoFromFsFile =
     pipe(
       stack.join(projectDir, file.path),
       task.chain(stack.getFileHash),
+      // fixme: should we use panic here?
       taskEither.getOrElse((e) => {
         throw e;
       }),
diff --git a/src/domain/FileSystem/Path.tests.ts b/src/domain/FileSystem/Path.tests.ts
new file mode 100644
index 00000000..8caa6f23
--- /dev/null
+++ b/src/domain/FileSystem/Path.tests.ts
@@ -0,0 +1,51 @@
+import { fc } from '@code-expert/test-utils';
+import { assert, describe, it } from 'vitest';
+import { iots } from '@code-expert/prelude';
+import { PfsPath, PfsPathBrand, isValidDirName, isValidFileName } from '@/domain/FileSystem';
+
+const wordCharBuilders = [
+  { num: 26, build: (v: number) => String.fromCharCode(v + 0x41) },
+  { num: 26, build: (v: number) => String.fromCharCode(v + 0x61) },
+  { num: 10, build: (v: number) => String.fromCharCode(v + 0x30) },
+  { num: 1, build: () => String.fromCharCode(0x5f) },
+];
+
+const fsNodeCharBuilders = [
+  ...wordCharBuilders,
+  { num: 0, build: () => String.fromCharCode(0x20) },
+  { num: 1, build: () => String.fromCharCode(0x2d) },
+];
+
+export const legalDirNameArb = fc.stringOf(fc.mapToConstant(...fsNodeCharBuilders), {
+  minLength: 1,
+  maxLength: 80,
+});
+
+export const legalFileNameArb = fc
+  .tuple(
+    fc.stringOf(fc.mapToConstant(...fsNodeCharBuilders), { minLength: 0, maxLength: 80 }),
+    fc.constant('.'),
+    fc.stringOf(fc.mapToConstant(...wordCharBuilders), { minLength: 1, maxLength: 5 }),
+  )
+  .map((elements) => elements.join(''));
+
+// todo: it is unclear how many "collisions" this produces, we might need a better solution
+export const pfsPathArb: fc.Arbitrary<PfsPath> = fc
+  .tuple(fc.array(legalDirNameArb), legalFileNameArb)
+  .map(([path, file]) => `./${path.join('/')}/${file}`)
+  .map(iots.brandFromLiteral<string, PfsPathBrand>);
+
+describe('PfsPath', () => {
+  describe('legalDirNameArb', () => {
+    it('should only produce strings that are accepted by isValidDirName', () => {
+      fc.assert(fc.property(legalDirNameArb, (dirName) => assert.isTrue(isValidDirName(dirName))));
+    });
+  });
+  describe('legalFileNameArb', () => {
+    it('should only produce strings that are accepted by isValidFileName', () => {
+      fc.assert(
+        fc.property(legalFileNameArb, (fileName) => assert.isTrue(isValidFileName(fileName))),
+      );
+    });
+  });
+});
diff --git a/src/domain/ProjectSync/apiStack.ts b/src/domain/ProjectSync/apiStack.ts
index 99257ec1..29a02076 100644
--- a/src/domain/ProjectSync/apiStack.ts
+++ b/src/domain/ProjectSync/apiStack.ts
@@ -20,7 +20,7 @@ export const apiStack: ApiStack = {
   readRemoteProjectFile: (projectId, file) =>
     apiGetSigned({
       path: `project/${projectId}/file`,
-      jwtPayload: { path: file },
+      jwtPayload: { path: file }, // fixme: add version
       codec: iots.Uint8ArrayC,
       responseType: ResponseType.Binary,
     }),
diff --git a/src/domain/ProjectSync/getLocalChanges.tests.ts b/src/domain/ProjectSync/getLocalChanges.tests.ts
new file mode 100644
index 00000000..c264ec9b
--- /dev/null
+++ b/src/domain/ProjectSync/getLocalChanges.tests.ts
@@ -0,0 +1,150 @@
+import { fc } from '@code-expert/test-utils';
+import { NonEmptyArray } from 'fp-ts/NonEmptyArray';
+import { Lens } from 'monocle-ts';
+import * as nodePath from 'path';
+import { assert, describe, it } from 'vitest';
+import { nonEmptyArray, option, pipe, task, taskEither, taskOption } from '@code-expert/prelude';
+import {
+  LocalFileChange,
+  LocalFileInfo,
+  getLocalChanges,
+  localChangeType,
+} from '@/domain/FileSystem';
+import { pfsPathArb } from '@/domain/FileSystem/Path.tests';
+import { FileSystemStack } from '@/domain/FileSystem/fileSystemStack';
+import { ordFsNode } from '@/lib/tauri/fs';
+import { escape } from '@/lib/tauri/path';
+import { panic } from '@/utils/error';
+
+const Hash = Lens.fromProp<LocalFileInfo>()('hash');
+const modifyHash = Hash.modify((h) => h + '2');
+
+export const nodeFsStack: FileSystemStack = {
+  dirname: (path) => taskEither.fromIO(() => nodePath.dirname(path)),
+  join: (...paths) => task.fromIO(() => nodePath.join(...paths)),
+  stripAncestor: (ancestor) => (to) =>
+    taskEither.fromIO(() => {
+      const relative = nodePath.relative(ancestor, to);
+      const normalized = nodePath.normalize(relative);
+      return nodePath.format({ dir: '.', base: normalized });
+    }),
+  escape,
+  getFileHash: () => panic('getFileHash is not implemented on nodeFsStack'),
+  removeFile: () => panic('removeFile is not implemented on nodeFsStack'),
+  basename: (path) => pipe(path.split('/'), (ps) => ps[ps.length - 1], taskOption.of),
+  tempDir: () => panic('tempDir is not implemented on nodeFsStack'),
+  readBinaryFile: () => panic('readBinaryFile is not implemented on nodeFsStack'),
+  readFsTree: () => panic('readFsTree is not implemented on nodeFsStack'),
+};
+
+const localFileInfoArb = fc.record<LocalFileInfo>({
+  type: fc.constant('file'),
+  path: pfsPathArb,
+  hash: fc.string({ minLength: 8, maxLength: 8 }),
+});
+
+describe('getLocalChanges', () => {
+  const toRemoved = (fileInfo: LocalFileInfo): LocalFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: localChangeType.removed(),
+  });
+  const toAdded = (fileInfo: LocalFileInfo): LocalFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: localChangeType.added(),
+  });
+  const toUpdated = (fileInfo: LocalFileInfo): LocalFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: localChangeType.updated(),
+  });
+
+  it('should classify missing files as "removed"', () => {
+    const commonFilesArb = fc.array(localFileInfoArb);
+    const missingFilesArb = fc.nonEmptyArray(localFileInfoArb);
+
+    const missingToRemoved = (
+      commonFiles: Array<LocalFileInfo>,
+      missingFiles: NonEmptyArray<LocalFileInfo>,
+    ) =>
+      assert.deepEqual(
+        getLocalChanges([...commonFiles, ...missingFiles], [...commonFiles]),
+        pipe(missingFiles, nonEmptyArray.map(toRemoved), option.some),
+      );
+
+    fc.assert(fc.property(commonFilesArb, missingFilesArb, missingToRemoved));
+  });
+
+  it('should classify new files as "added"', () => {
+    const commonFilesArb = fc.array(localFileInfoArb);
+    const newFilesArb = fc.nonEmptyArray(localFileInfoArb);
+
+    const newToAdded = (
+      commonFiles: Array<LocalFileInfo>,
+      newFiles: NonEmptyArray<LocalFileInfo>,
+    ) =>
+      assert.deepEqual(
+        getLocalChanges([...commonFiles], [...commonFiles, ...newFiles]),
+        pipe(newFiles, nonEmptyArray.map(toAdded), option.some),
+      );
+
+    fc.assert(fc.property(commonFilesArb, newFilesArb, newToAdded));
+  });
+
+  it('should classify files with a different version as "updated"', () => {
+    const commonFilesArb = fc.array(localFileInfoArb);
+    const changedFilesArb = fc.nonEmptyArray(localFileInfoArb);
+
+    const changedToUpdated = (
+      commonFiles: Array<LocalFileInfo>,
+      changedFiles: NonEmptyArray<LocalFileInfo>,
+    ) =>
+      assert.deepEqual(
+        getLocalChanges(
+          [...commonFiles, ...changedFiles],
+          [...commonFiles, ...changedFiles.map(modifyHash)],
+        ),
+        pipe(changedFiles, nonEmptyArray.map(toUpdated), option.some),
+      );
+
+    fc.assert(fc.property(commonFilesArb, changedFilesArb, changedToUpdated));
+  });
+
+  it('should do all three at the same time', () => {
+    const commonFilesArb = fc.array(localFileInfoArb);
+    const missingFilesArb = fc.nonEmptyArray(localFileInfoArb);
+    const newFilesArb = fc.nonEmptyArray(localFileInfoArb);
+    const changedFilesArb = fc.nonEmptyArray(localFileInfoArb);
+
+    const removedNewChanged = (
+      commonFiles: Array<LocalFileInfo>,
+      missingFiles: NonEmptyArray<LocalFileInfo>,
+      newFiles: NonEmptyArray<LocalFileInfo>,
+      changedFiles: NonEmptyArray<LocalFileInfo>,
+    ) =>
+      assert.deepEqual(
+        pipe(
+          getLocalChanges(
+            [...commonFiles, ...missingFiles, ...changedFiles],
+            [...commonFiles, ...newFiles, ...changedFiles.map(modifyHash)],
+          ),
+          option.map(nonEmptyArray.sort<LocalFileChange>(ordFsNode)),
+        ),
+        pipe(
+          [
+            nonEmptyArray.map(toRemoved)(missingFiles),
+            nonEmptyArray.map(toAdded)(newFiles),
+            nonEmptyArray.map(toUpdated)(changedFiles),
+          ],
+          nonEmptyArray.concatAll(nonEmptyArray.getSemigroup()),
+          nonEmptyArray.sort<LocalFileChange>(ordFsNode),
+          option.some,
+        ),
+      );
+
+    fc.assert(
+      fc.property(commonFilesArb, missingFilesArb, newFilesArb, changedFilesArb, removedNewChanged),
+    );
+  });
+});
diff --git a/src/domain/ProjectSync/getRemoteChanges.tests.ts b/src/domain/ProjectSync/getRemoteChanges.tests.ts
new file mode 100644
index 00000000..c52f74cf
--- /dev/null
+++ b/src/domain/ProjectSync/getRemoteChanges.tests.ts
@@ -0,0 +1,154 @@
+import { fc } from '@code-expert/test-utils';
+import { NonEmptyArray } from 'fp-ts/NonEmptyArray';
+import { Lens } from 'monocle-ts';
+import { assert, describe, it } from 'vitest';
+import { nonEmptyArray, option, pipe } from '@code-expert/prelude';
+import {
+  RemoteDirInfo,
+  RemoteFileChange,
+  RemoteFileInfo,
+  RemoteNodeInfo,
+  getRemoteChanges,
+  remoteChangeType,
+} from '@/domain/FileSystem';
+import { pfsPathArb } from '@/domain/FileSystem/Path.tests';
+import { ordFsNode } from '@/lib/tauri/fs';
+
+const Version = Lens.fromProp<RemoteNodeInfo>()('version');
+const incrementVersion = Version.modify((v) => v + 1);
+
+const remoteFileInfoArb = fc.record<RemoteFileInfo>({
+  type: fc.constant('file'),
+  path: pfsPathArb,
+  version: fc.nat(),
+  permissions: fc.constantFrom('r', 'rw'),
+});
+
+const remoteDirInfoArb = fc.record<RemoteDirInfo>({
+  type: fc.constant('dir'),
+  path: pfsPathArb,
+  version: fc.nat(),
+  permissions: fc.constantFrom('r', 'rw'),
+});
+
+describe('getRemoteChanges', () => {
+  const toRemoved = (fileInfo: RemoteFileInfo): RemoteFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: remoteChangeType.removed(),
+  });
+  const toAdded = (fileInfo: RemoteFileInfo): RemoteFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: remoteChangeType.added(fileInfo.version),
+  });
+  const toUpdated = (fileInfo: RemoteFileInfo): RemoteFileChange => ({
+    path: fileInfo.path,
+    type: 'file',
+    change: remoteChangeType.updated(fileInfo.version),
+  });
+
+  it('should classify missing files as "removed"', () => {
+    const dirsArb = fc.array(remoteDirInfoArb);
+    const commonFilesArb = fc.array(remoteFileInfoArb);
+    const missingFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+
+    const missingToRemoved = (
+      dirs: Array<RemoteDirInfo>,
+      commonFiles: Array<RemoteFileInfo>,
+      missingFiles: NonEmptyArray<RemoteFileInfo>,
+    ) =>
+      assert.deepEqual(
+        // fixme: does concat order matter? how do we make it not matter?
+        getRemoteChanges([...commonFiles, ...missingFiles], [...commonFiles, ...dirs]),
+        pipe(missingFiles, nonEmptyArray.map(toRemoved), option.some),
+      );
+
+    fc.assert(fc.property(dirsArb, commonFilesArb, missingFilesArb, missingToRemoved));
+  });
+
+  it('should classify new files as "added"', () => {
+    const dirsArb = fc.array(remoteDirInfoArb);
+    const commonFilesArb = fc.array(remoteFileInfoArb);
+    const newFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+
+    const newToAdded = (
+      dirs: Array<RemoteDirInfo>,
+      commonFiles: Array<RemoteFileInfo>,
+      newFiles: NonEmptyArray<RemoteFileInfo>,
+    ) =>
+      assert.deepEqual(
+        getRemoteChanges([...commonFiles], [...commonFiles, ...dirs, ...newFiles]),
+        pipe(newFiles, nonEmptyArray.map(toAdded), option.some),
+      );
+
+    fc.assert(fc.property(dirsArb, commonFilesArb, newFilesArb, newToAdded));
+  });
+
+  it('should classify files with a different version as "updated"', () => {
+    const dirsArb = fc.array(remoteDirInfoArb);
+    const commonFilesArb = fc.array(remoteFileInfoArb);
+    const changedFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+
+    const changedToUpdated = (
+      dirs: Array<RemoteDirInfo>,
+      commonFiles: Array<RemoteFileInfo>,
+      changedFiles: NonEmptyArray<RemoteFileInfo>,
+    ) =>
+      assert.deepEqual(
+        getRemoteChanges(
+          [...commonFiles, ...changedFiles],
+          [...commonFiles, ...dirs, ...changedFiles.map(incrementVersion)],
+        ),
+        pipe(changedFiles, nonEmptyArray.map(toUpdated), option.some),
+      );
+
+    fc.assert(fc.property(dirsArb, commonFilesArb, changedFilesArb, changedToUpdated));
+  });
+
+  it('should do all three at the same time', () => {
+    const dirsArb = fc.array(remoteDirInfoArb);
+    const commonFilesArb = fc.array(remoteFileInfoArb);
+    const missingFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+    const newFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+    const changedFilesArb = fc.nonEmptyArray(remoteFileInfoArb);
+
+    const removedNewChanged = (
+      dirs: Array<RemoteDirInfo>,
+      commonFiles: Array<RemoteFileInfo>,
+      missingFiles: NonEmptyArray<RemoteFileInfo>,
+      newFiles: NonEmptyArray<RemoteFileInfo>,
+      changedFiles: NonEmptyArray<RemoteFileInfo>,
+    ) =>
+      assert.deepEqual(
+        pipe(
+          getRemoteChanges(
+            [...commonFiles, ...missingFiles, ...changedFiles],
+            [...commonFiles, ...dirs, ...newFiles, ...changedFiles.map(incrementVersion)],
+          ),
+          option.map(nonEmptyArray.sort<RemoteFileChange>(ordFsNode)),
+        ),
+        pipe(
+          [
+            nonEmptyArray.map(toRemoved)(missingFiles),
+            nonEmptyArray.map(toAdded)(newFiles),
+            nonEmptyArray.map(toUpdated)(changedFiles),
+          ],
+          nonEmptyArray.concatAll(nonEmptyArray.getSemigroup()),
+          nonEmptyArray.sort<RemoteFileChange>(ordFsNode),
+          option.some,
+        ),
+      );
+
+    fc.assert(
+      fc.property(
+        dirsArb,
+        commonFilesArb,
+        missingFilesArb,
+        newFilesArb,
+        changedFilesArb,
+        removedNewChanged,
+      ),
+    );
+  });
+});