get_theme_root_uri() returns a file path, not URI

I followed this guide to set up WordPress testing environment: https://make.www.ads-software.com/core/handbook/testing/automated-testing/phpunit/

When I’m running tests with PHPUnit, I receive a lot of ‘F’s, especially for this file:
tests\phpunit\tests\link\themeFile.php:161

1) Tests_Link_ThemeFile::test_theme_file_uri_returns_valid_uri with data set #0 ('parent-only.php', 'theme-file-parent', array('theme-file-parent'))
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-''
+'C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1/default/parent-only.php'

This is because get_theme_file_uri( $file ) returns file path (C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1/default/parent-only.php) instead of URI.

I debugged it, and I can see that get_site_transient( 'theme_roots' ) returns:

Array
(
    [block-theme] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [broken-theme] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [camelCase] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [child-parent-itself] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [default] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [internationalized-theme] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [page-templates-child] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [page-templates] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [rest-api] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [sandbox] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [stylesheetonly] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [subdir/theme with spaces] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [subdir/theme2] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [theme1-dupe] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [theme1] => C:\DevTools\xampp\htdocs\wptestsuite.local\tests\phpunit\includes/../data/themedir1
    [twentyeleven] => /themes
    [twentyfifteen] => /themes
    [twentyfourteen] => /themes
    [twentynineteen] => /themes
    [twentyseventeen] => /themes
    [twentysixteen] => /themes
    [twentyten] => /themes
    [twentythirteen] => /themes
    [twentytwelve] => /themes
    [twentytwenty] => /themes
    [twentytwentyone] => /themes
)

It has to return correct URI for each value, or part of it. For the above ones, it returns absolute path.

What am I missing?