langium: additional tests of UriUtils.relative() with windows paths (#1805)

* they're executed on windows only and skipped for all other platforms, because of https://github.com/microsoft/vscode-uri/blob/edfdccd976efaf4bb8fdeca87e97c47257721729/src/uri.ts#L309-L311

Author: sailingKieler

packages/langium/test/utils/uri-utils.test.ts

@@ -21,18 +21,36 @@ describe('URI Utils', () => {
         expect(UriUtils.relative(from, to)).toBe('../d.txt');
     });
 
+    test.skipIf(process.platform !== 'win32')('relative path in parent directory win32', () => {
+        const from = URI.file('c:\\a\\b');
+        const to = URI.file('c:\\a\\d.txt');
+        expect(UriUtils.relative(from, to)).toBe('../d.txt');
+    });
+
     test('relative path in sub directory', () => {
         const from = URI.file('/a');
         const to = URI.file('/a/b/c.txt');
         expect(UriUtils.relative(from, to)).toBe('b/c.txt');
     });
 
+    test.skipIf(process.platform !== 'win32')('relative path in sub directory win32', () => {
+        const from = URI.file('c:\\a');
+        const to = URI.file('c:\\a\\b\\c.txt');
+        expect(UriUtils.relative(from, to)).toBe('b/c.txt');
+    });
+
     test('relative path in other directory', () => {
         const from = URI.file('/a/b');
         const to = URI.file('/a/c/d.txt');
         expect(UriUtils.relative(from, to)).toBe('../c/d.txt');
     });
 
+    test.skipIf(process.platform !== 'win32')('relative path in other directory win32', () => {
+        const from = URI.file('c:\\a\\b');
+        const to = URI.file('c:\\a\\c\\d.txt');
+        expect(UriUtils.relative(from, to)).toBe('../c/d.txt');
+    });
+
     test('Equal uris are equal', () => {
         const uri1 = 'file:///a/b';
         const uri2 = 'file:///a/b';