Asset discovery failing with "Snapshots must have a resource with 'is-root' true.If more than one is provided"

[itsjwala]

The problem

@pytest.mark.parametrize("url, test_name", ([
    ["https://abc.com/one", "test_1"],
    ["https://abc.com/two", "test_2"],
    ["https://abc.com/three", "test_3"],
    ["https://abc.com/four", "test_4"],
]))
def test_screen_1(url, test_name):
    driver = webdriver.Chrome(executable_path ="/path")
    driver.get(url)
    time.sleep(3)
    percy_snapshot(driver, test_name)
    driver.quit()

consider above example, where in test_1 snapshot is a root resource and is being cached while doing asset discovery in below code line.

cli/packages/core/src/discovery.js

Lines 281 to 282 in cf1bae8

	getResource: u => snapshot.resources.get(u) || cache.get(u),
	saveResource: r => snapshot.resources.set(r.url, r) && cache.set(r.url, r)

when we take snapshots for other URLs say https://abc.com/three, https://abc.com/one is being referenced in the webpage.

and causes us to serve a dirty cache from the previous snapshot for which is-root was true.

Possible Solution

• We need to invalidate such cross-snapshot resources cache or have stricter checks