Add seek test

Author: rhpvorderman

tests/test_igzip.py

@@ -460,6 +460,44 @@ def test_concatenated_gzip():
     assert data == result
 
 
+def test_seek():
+    from io import SEEK_CUR, SEEK_END, SEEK_SET
+    with tempfile.NamedTemporaryFile("wb") as tmpfile:
+        tmpfile.write(gzip.compress(b"X" * 500 + b"A" + b"X" * 499))
+        tmpfile.write(gzip.compress(b"X" * 500 + b"B" + b"X" * 499))
+        tmpfile.write(gzip.compress(b"X" * 500 + b"C" + b"X" * 499))
+        tmpfile.write(gzip.compress(b"X" * 500 + b"D" + b"X" * 499))
+        tmpfile.flush()
+        with igzip.open(tmpfile.name, "rb") as gzip_file:
+            # Start testing forward seek
+            gzip_file.seek(500)
+            assert gzip_file.read(1) == b"A"
+            gzip_file.seek(1500)# Any positive number should end up at the end
+            assert gzip_file.read(1) == b"B"
+            # Test reverse
+            gzip_file.seek(500)
+            assert gzip_file.read(1) == b"A"
+            # Again, but with explicit SEEK_SET
+            gzip_file.seek(500, SEEK_SET)
+            assert gzip_file.read(1) == b"A"
+            gzip_file.seek(1500, SEEK_SET)
+            assert gzip_file.read(1) == b"B"
+            gzip_file.seek(500, SEEK_SET)
+            assert gzip_file.read(1) == b"A"
+            # Seeking from current position
+            gzip_file.seek(500)
+            gzip_file.seek(2000, SEEK_CUR)
+            assert gzip_file.read(1) == b"C"
+            gzip_file.seek(-1001, SEEK_CUR)
+            assert gzip_file.read(1) == b"B"
+            # Seeking from end
+            # Any positive number should end up at the end
+            gzip_file.seek(200, SEEK_END)
+            assert gzip_file.read(1) == b""
+            gzip_file.seek(-1500, SEEK_END)
+            assert gzip_file.read(1) == b"C"
+
+
 def test_bgzip():
     bgzip_file = Path(__file__).parent / "data" / "test.fastq.bgzip.gz"
     gzip_file = Path(__file__).parent / "data" / "test.fastq.gz"