Add a test case for reading FLAC files over HTTP.

We want to be sure that the soundfile library is compatible with
wfdb.io._url.NetFile, since wfdb.io._signal._rd_compressed_file relies
on this.

This isn't a complete test of WFDB/FLAC functionality, in part because
the sample files are very small so we can't really exercise the
seeking functionality.  However, this should be sufficient to verify
that soundfile doesn't make silly assumptions (like assuming the input
file corresponds to an OS file descriptor.)

tests/test_url.py

@@ -196,6 +196,62 @@ def _test_binary(self, url, content, buffering):
             self.assertEqual(bf.tell(), len(content))
 
 
+class TestRemoteFLACFiles(unittest.TestCase):
+    """
+    Test reading FLAC files over HTTP.
+    """
+
+    def test_whole_file(self):
+        """
+        Test reading a complete FLAC file using local and HTTP APIs.
+
+        This tests that we can read the file 'sample-data/flacformats.d2'
+        (a 24-bit FLAC stream) using the soundfile library, first by
+        reading the file from the local filesystem, and then using
+        wfdb.io._url.openurl() to access it through a simulated web server.
+
+        This is meant to verify that the soundfile library works using only
+        the standard Python file object API (as implemented by
+        wfdb.io._url.NetFile), and doesn't require the input file to be an
+        actual io.FileIO object.
+
+        Parameters
+        ----------
+        N/A
+
+        Returns
+        -------
+        N/A
+
+        """
+        import soundfile
+        import numpy as np
+
+        data_file_path = "sample-data/flacformats.d2"
+        expected_format = "FLAC"
+        expected_subtype = "PCM_24"
+
+        # Read the file using standard file I/O
+        sf1 = soundfile.SoundFile(data_file_path)
+        self.assertEqual(sf1.format, expected_format)
+        self.assertEqual(sf1.subtype, expected_subtype)
+        data1 = sf1.read()
+
+        # Read the file using HTTP
+        with open(data_file_path, "rb") as f:
+            file_content = {"/foo.dat": f.read()}
+        with DummyHTTPServer(file_content) as server:
+            url = server.url("/foo.dat")
+            file2 = wfdb.io._url.openurl(url, "rb")
+            sf2 = soundfile.SoundFile(file2)
+            self.assertEqual(sf2.format, expected_format)
+            self.assertEqual(sf2.subtype, expected_subtype)
+            data2 = sf2.read()
+
+        # Check that results are equal
+        np.testing.assert_array_equal(data1, data2)
+
+
 class DummyHTTPServer(http.server.HTTPServer):
     """
     HTTPServer used to simulate a web server for testing.