Add PathFragment tests for mixed Windows path separators.

To clarify that this is working as intended.

Closes #22343.

PiperOrigin-RevId: 633557654
Change-Id: I1b029d285626b0f87d0206eac68aa438ca24f014

src/test/java/com/google/devtools/build/lib/vfs/PathFragmentWindowsTest.java

@@ -177,6 +177,9 @@ public void testGetParentDirectoryWindows() {
   public void testSegmentsCountWindows() {
     assertThat(create("C:/foo").segmentCount()).isEqualTo(1);
     assertThat(create("C:/").segmentCount()).isEqualTo(0);
+    // Mix usage of Windows and Unix separator is valid
+    assertThat(create("C:/foo\\bar").segmentCount()).isEqualTo(2);
+    assertThat(create("C:\\foo\\bar/baz").segmentCount()).isEqualTo(3);
   }
 
   @Test
@@ -185,6 +188,12 @@ public void testGetSegmentWindows() {
     assertThat(create("C:/foo/bar").getSegment(1)).isEqualTo("bar");
     assertThat(create("C:/foo/").getSegment(0)).isEqualTo("foo");
     assertThat(create("C:/foo").getSegment(0)).isEqualTo("foo");
+    // Mix usage of Windows and Unix separator is valid
+    assertThat(create("C:/foo\\bar").getSegment(0)).isEqualTo("foo");
+    assertThat(create("C:/foo\\bar").getSegment(1)).isEqualTo("bar");
+    assertThat(create("C:\\foo\\bar/baz").getSegment(0)).isEqualTo("foo");
+    assertThat(create("C:\\foo\\bar/baz").getSegment(1)).isEqualTo("bar");
+    assertThat(create("C:\\foo\\bar/baz").getSegment(2)).isEqualTo("baz");
   }
 
   @Test
@@ -193,6 +202,9 @@ public void testBasenameWindows() throws Exception {
     assertThat(create("C:/foo").getBaseName()).isEqualTo("foo");
     // Never return the drive name as a basename.
     assertThat(create("C:/").getBaseName()).isEmpty();
+    // Mix usage of Windows and Unix separator is valid
+    assertThat(create("C:/foo\\bar").getBaseName()).isEqualTo("bar");
+    assertThat(create("C:\\foo\\bar/baz").getBaseName()).isEqualTo("baz");
   }
 
   @Test