value, ok := LookupEnv(smallpox) // Should not exist.
	if ok || value != "" {
		t.Fatalf("%s=%q", smallpox, value)
	}
	defer Unsetenv(smallpox)
	err := Setenv(smallpox, "virus")
	if err != nil {
		t.Fatalf("failed to release smallpox virus")
	}
	_, ok = LookupEnv(smallpox)
	if !ok {
		t.Errorf("smallpox release failed; world remains safe but LookupEnv is broken")
	}
}

#
# Before Go 1.16, we extracted each module zip to a temporary directory with
# a random name, then renamed that into place with os.Rename. On Windows,
# this failed with ERROR_ACCESS_DENIED when another process (usually an
# anti-virus scanner) opened files in the temporary directory. This test
# simulates that behavior, verifying golang.org/issue/36568.
#
# Since 1.16, we extract to the final directory, but we create a .partial file