Add integration tests

Tests if repository json files conform to the json schema.
If all resources (images/icons/website URLs) they mention actually
exists.

And can also test writing images and the FAT modification code.

tests/conftest.py

@@ -0,0 +1,90 @@
+import pytest
+import json
+import urllib.request
+
+os_list_files = []
+icon_urls = set()
+website_urls = set()
+item_json = []
+already_processed_urls = set()
+total_download_size = 0
+largest_extract_size = 0
+
+def pytest_addoption(parser):
+    parser.addoption(
+        "--repo",
+        action="store",
+        default="https://downloads.raspberrypi.com/os_list_imagingutility_v3.json",
+        help="Repository URL to test"
+    )
+    parser.addoption(
+        "--device",
+        action="store",
+        default="",
+        help="(Loop) device if you want to perform actual image write tests"
+    )
+
+def parse_json_entries(j):
+    global total_download_size, largest_extract_size
+
+    for item in j:
+        if "subitems" in item:
+            parse_json_entries(item["subitems"])
+        elif "subitems_url" in item:
+            parse_os_list(item["subitems_url"])
+        else:
+            if "icon" in item and not item["icon"].startswith("data:"):
+                icon_urls.add(item["icon"])
+            if "website" in item:
+                website_urls.add(item["website"])
+            if "url" in item:
+                item_json.append(item)
+            if "image_download_size" in item:
+                total_download_size += int(item["image_download_size"])
+            if "extract_size" in item:
+                largest_extract_size = max(largest_extract_size, int(item["extract_size"]))
+
+def parse_os_list(url):
+    if url in already_processed_urls:
+        print("Circular reference! Already processed URL: {}".format(url))
+        return
+
+    already_processed_urls.add(url)
+
+    try:
+        print("Fetching OS list file {}".format(url))
+        req = urllib.request.Request(
+            url, 
+            data=None, 
+            headers={
+                'User-Agent': 'rpi-imager automated tests'
+            }
+        )
+        response = urllib.request.urlopen(req)
+        body = response.read()
+        j = json.loads(body)
+        os_list_files.append( (url,body) )
+
+        if "os_list" in j:
+            parse_json_entries(j["os_list"])
+
+    except Exception as err:
+        print("Error processing '{}': {}".format(url, repr(err) ))
+
+def pytest_configure(config):
+    parse_os_list(config.getoption("--repo"))
+    print("Found {} os_list.json files {} OS images {} icons {} website URLs".format( 
+        len(os_list_files), len(item_json), len(icon_urls), len(website_urls) ) )
+    print("Total compressed image download size: {} GB".format(round(total_download_size / 1024 ** 3) ))
+    print("Largest uncompressed image size: {} GB".format(round(largest_extract_size / 1024 ** 3) ))
+
+
+def pytest_generate_tests(metafunc):
+    if "oslisttuple" in metafunc.fixturenames:
+        metafunc.parametrize("oslisttuple", os_list_files)
+    if "iconurl" in metafunc.fixturenames:
+        metafunc.parametrize("iconurl", icon_urls)
+    if "websiteurl" in metafunc.fixturenames:
+        metafunc.parametrize("websiteurl", website_urls)
+    if "imageitem" in metafunc.fixturenames:
+        metafunc.parametrize("imageitem", item_json)