sources: add tiny unit test for inline source fechting

This commit adds a small unit test that the inline source
works as expected by creating some test_data and then
checking that it ends up in the cache.

Note that this is also already tested in the tests in
osbuild/test/run/test_sources.py but there its a lot more
indirect and in the spirit of tests-as-documentation having
an explicit test here seems useful (its also quicker to
run and easier to discover).

Small followup for https://github.com/osbuild/osbuild/pull/2090
where this was discussed originally.

sources/test/test_inline.py

@@ -0,0 +1,33 @@
+import binascii
+import hashlib
+import lzma
+
+import pytest
+
+SOURCES_NAME = "org.osbuild.inline"
+
+
+@pytest.mark.parametrize("encoding", ["base64", "lzma+base64"])
+def test_inline_fetch(tmp_path, sources_service, encoding):
+    test_data = b"1234"
+    hasher = hashlib.new("sha256")
+    hasher.update(test_data)
+    if encoding == "base64":
+        encoded_data = binascii.b2a_base64(test_data)
+    elif encoding == "lzma+base64":
+        encoded_data = binascii.b2a_base64(lzma.compress(test_data))
+    else:
+        raise ValueError(f"unsupported encoding {encoding}")
+
+    test_data_chksum = f"sha256:{hasher.hexdigest()}"
+    TEST_SOURCES = {
+        test_data_chksum: {
+            "encoding": encoding,
+            "data": encoded_data,
+        },
+    }
+    sources_service.cache = tmp_path / "cachedir"
+    sources_service.cache.mkdir()
+    sources_service.tmpdir = tmp_path
+    sources_service.fetch_all(TEST_SOURCES)
+    assert (sources_service.cache / test_data_chksum).read_bytes() == test_data