Improve user messages

src/dnaio/_bam.py

@@ -6,13 +6,13 @@ def read_bam_header(fileobj: BufferedIOBase) -> bytes:
     magic = fileobj.read(4)
     if not isinstance(magic, bytes):
         raise TypeError(
-            f"fileobj {fileobj} is not a binary IO type, " f"got {type(fileobj)}"
+            f"fileobj {fileobj} (type: {type(fileobj)}), was not opened in binary mode."
         )
     if len(magic) < 4:
         raise EOFError("Truncated BAM file")
     if magic[:4] != b"BAM\1":
         raise ValueError(
-            f"fileobj: {fileobj}, is not a BAM file. No BAM magic, instead "
+            f"fileobj: {fileobj}, is not a BAM file. No BAM file signature, instead "
             f"found {magic!r}"
         )
     return read_bam_header_after_magic(fileobj)

tests/test_internal.py

@@ -785,7 +785,7 @@ def test_bam_parser_not_binary_error(self):
         )
         with pytest.raises(TypeError) as error:
             BamReader(file)
-        error.match("binary IO")
+        error.match("binary mode")
 
     @pytest.mark.parametrize("buffersize", [4, 8, 10, 20, 40])
     def test_small_buffersize(self, buffersize):