diff --git a/Tests/images/hopper_long_name.im b/Tests/images/hopper_long_name.im
new file mode 100644
index 00000000000..ff45b7c7539
Binary files /dev/null and b/Tests/images/hopper_long_name.im differ
diff --git a/Tests/test_file_bmp.py b/Tests/test_file_bmp.py
index b3a01b95a07..8bb58794c00 100644
--- a/Tests/test_file_bmp.py
+++ b/Tests/test_file_bmp.py
@@ -1,128 +1,139 @@
 import io
 
+import pytest
 from PIL import BmpImagePlugin, Image
 
-from .helper import PillowTestCase, assert_image_equal, hopper
+from .helper import assert_image_equal, hopper
 
 
-class TestFileBmp(PillowTestCase):
-    def roundtrip(self, im):
-        outfile = self.tempfile("temp.bmp")
+def test_sanity(tmp_path):
+    def roundtrip(im):
+        outfile = str(tmp_path / "temp.bmp")
 
         im.save(outfile, "BMP")
 
         with Image.open(outfile) as reloaded:
             reloaded.load()
-            self.assertEqual(im.mode, reloaded.mode)
-            self.assertEqual(im.size, reloaded.size)
-            self.assertEqual(reloaded.format, "BMP")
-            self.assertEqual(reloaded.get_format_mimetype(), "image/bmp")
-
-    def test_sanity(self):
-        self.roundtrip(hopper())
-
-        self.roundtrip(hopper("1"))
-        self.roundtrip(hopper("L"))
-        self.roundtrip(hopper("P"))
-        self.roundtrip(hopper("RGB"))
-
-    def test_invalid_file(self):
-        with open("Tests/images/flower.jpg", "rb") as fp:
-            self.assertRaises(SyntaxError, BmpImagePlugin.BmpImageFile, fp)
-
-    def test_save_to_bytes(self):
-        output = io.BytesIO()
-        im = hopper()
-        im.save(output, "BMP")
-
-        output.seek(0)
-        with Image.open(output) as reloaded:
-            self.assertEqual(im.mode, reloaded.mode)
-            self.assertEqual(im.size, reloaded.size)
-            self.assertEqual(reloaded.format, "BMP")
-
-    def test_save_too_large(self):
-        outfile = self.tempfile("temp.bmp")
-        with Image.new("RGB", (1, 1)) as im:
-            im._size = (37838, 37838)
-            with self.assertRaises(ValueError):
-                im.save(outfile)
-
-    def test_dpi(self):
-        dpi = (72, 72)
-
-        output = io.BytesIO()
-        with hopper() as im:
-            im.save(output, "BMP", dpi=dpi)
-
-        output.seek(0)
-        with Image.open(output) as reloaded:
-            self.assertEqual(reloaded.info["dpi"], dpi)
-
-    def test_save_bmp_with_dpi(self):
-        # Test for #1301
-        # Arrange
-        outfile = self.tempfile("temp.jpg")
-        with Image.open("Tests/images/hopper.bmp") as im:
-
-            # Act
-            im.save(outfile, "JPEG", dpi=im.info["dpi"])
-
-            # Assert
-            with Image.open(outfile) as reloaded:
-                reloaded.load()
-                self.assertEqual(im.info["dpi"], reloaded.info["dpi"])
-                self.assertEqual(im.size, reloaded.size)
-                self.assertEqual(reloaded.format, "JPEG")
-
-    def test_load_dpi_rounding(self):
-        # Round up
-        with Image.open("Tests/images/hopper.bmp") as im:
-            self.assertEqual(im.info["dpi"], (96, 96))
-
-        # Round down
-        with Image.open("Tests/images/hopper_roundDown.bmp") as im:
-            self.assertEqual(im.info["dpi"], (72, 72))
-
-    def test_save_dpi_rounding(self):
-        outfile = self.tempfile("temp.bmp")
-        with Image.open("Tests/images/hopper.bmp") as im:
-            im.save(outfile, dpi=(72.2, 72.2))
-            with Image.open(outfile) as reloaded:
-                self.assertEqual(reloaded.info["dpi"], (72, 72))
-
-            im.save(outfile, dpi=(72.8, 72.8))
-        with Image.open(outfile) as reloaded:
-            self.assertEqual(reloaded.info["dpi"], (73, 73))
+            assert im.mode == reloaded.mode
+            assert im.size == reloaded.size
+            assert reloaded.format == "BMP"
+            assert reloaded.get_format_mimetype() == "image/bmp"
+
+    roundtrip(hopper())
+
+    roundtrip(hopper("1"))
+    roundtrip(hopper("L"))
+    roundtrip(hopper("P"))
+    roundtrip(hopper("RGB"))
+
 
-    def test_load_dib(self):
-        # test for #1293, Imagegrab returning Unsupported Bitfields Format
-        with Image.open("Tests/images/clipboard.dib") as im:
-            self.assertEqual(im.format, "DIB")
-            self.assertEqual(im.get_format_mimetype(), "image/bmp")
+def test_invalid_file():
+    with open("Tests/images/flower.jpg", "rb") as fp:
+        with pytest.raises(SyntaxError):
+            BmpImagePlugin.BmpImageFile(fp)
 
-            with Image.open("Tests/images/clipboard_target.png") as target:
-                assert_image_equal(im, target)
 
-    def test_save_dib(self):
-        outfile = self.tempfile("temp.dib")
+def test_save_to_bytes():
+    output = io.BytesIO()
+    im = hopper()
+    im.save(output, "BMP")
 
-        with Image.open("Tests/images/clipboard.dib") as im:
+    output.seek(0)
+    with Image.open(output) as reloaded:
+        assert im.mode == reloaded.mode
+        assert im.size == reloaded.size
+        assert reloaded.format == "BMP"
+
+
+def test_save_too_large(tmp_path):
+    outfile = str(tmp_path / "temp.bmp")
+    with Image.new("RGB", (1, 1)) as im:
+        im._size = (37838, 37838)
+        with pytest.raises(ValueError):
             im.save(outfile)
 
-            with Image.open(outfile) as reloaded:
-                self.assertEqual(reloaded.format, "DIB")
-                self.assertEqual(reloaded.get_format_mimetype(), "image/bmp")
-                assert_image_equal(im, reloaded)
 
-    def test_rgba_bitfields(self):
-        # This test image has been manually hexedited
-        # to change the bitfield compression in the header from XBGR to RGBA
-        with Image.open("Tests/images/rgb32bf-rgba.bmp") as im:
+def test_dpi():
+    dpi = (72, 72)
+
+    output = io.BytesIO()
+    with hopper() as im:
+        im.save(output, "BMP", dpi=dpi)
+
+    output.seek(0)
+    with Image.open(output) as reloaded:
+        assert reloaded.info["dpi"] == dpi
+
+
+def test_save_bmp_with_dpi(tmp_path):
+    # Test for #1301
+    # Arrange
+    outfile = str(tmp_path / "temp.jpg")
+    with Image.open("Tests/images/hopper.bmp") as im:
+
+        # Act
+        im.save(outfile, "JPEG", dpi=im.info["dpi"])
+
+        # Assert
+        with Image.open(outfile) as reloaded:
+            reloaded.load()
+            assert im.info["dpi"] == reloaded.info["dpi"]
+            assert im.size == reloaded.size
+            assert reloaded.format == "JPEG"
+
+
+def test_load_dpi_rounding():
+    # Round up
+    with Image.open("Tests/images/hopper.bmp") as im:
+        assert im.info["dpi"] == (96, 96)
 
-            # So before the comparing the image, swap the channels
-            b, g, r = im.split()[1:]
-            im = Image.merge("RGB", (r, g, b))
+    # Round down
+    with Image.open("Tests/images/hopper_roundDown.bmp") as im:
+        assert im.info["dpi"] == (72, 72)
 
-        with Image.open("Tests/images/bmp/q/rgb32bf-xbgr.bmp") as target:
+
+def test_save_dpi_rounding(tmp_path):
+    outfile = str(tmp_path / "temp.bmp")
+    with Image.open("Tests/images/hopper.bmp") as im:
+        im.save(outfile, dpi=(72.2, 72.2))
+        with Image.open(outfile) as reloaded:
+            assert reloaded.info["dpi"] == (72, 72)
+
+        im.save(outfile, dpi=(72.8, 72.8))
+    with Image.open(outfile) as reloaded:
+        assert reloaded.info["dpi"] == (73, 73)
+
+
+def test_load_dib():
+    # test for #1293, Imagegrab returning Unsupported Bitfields Format
+    with Image.open("Tests/images/clipboard.dib") as im:
+        assert im.format == "DIB"
+        assert im.get_format_mimetype() == "image/bmp"
+
+        with Image.open("Tests/images/clipboard_target.png") as target:
             assert_image_equal(im, target)
+
+
+def test_save_dib(tmp_path):
+    outfile = str(tmp_path / "temp.dib")
+
+    with Image.open("Tests/images/clipboard.dib") as im:
+        im.save(outfile)
+
+        with Image.open(outfile) as reloaded:
+            assert reloaded.format == "DIB"
+            assert reloaded.get_format_mimetype() == "image/bmp"
+            assert_image_equal(im, reloaded)
+
+
+def test_rgba_bitfields():
+    # This test image has been manually hexedited
+    # to change the bitfield compression in the header from XBGR to RGBA
+    with Image.open("Tests/images/rgb32bf-rgba.bmp") as im:
+
+        # So before the comparing the image, swap the channels
+        b, g, r = im.split()[1:]
+        im = Image.merge("RGB", (r, g, b))
+
+    with Image.open("Tests/images/bmp/q/rgb32bf-xbgr.bmp") as target:
+        assert_image_equal(im, target)
diff --git a/Tests/test_file_im.py b/Tests/test_file_im.py
index ec046020ed3..30a9fd52a07 100644
--- a/Tests/test_file_im.py
+++ b/Tests/test_file_im.py
@@ -1,89 +1,110 @@
-import unittest
+import filecmp
 
 import pytest
 from PIL import Image, ImImagePlugin
 
-from .helper import PillowTestCase, assert_image_equal, hopper, is_pypy
+from .helper import assert_image_equal, hopper, is_pypy
 
 # sample im
 TEST_IM = "Tests/images/hopper.im"
 
 
-class TestFileIm(PillowTestCase):
-    def test_sanity(self):
+def test_sanity():
+    with Image.open(TEST_IM) as im:
+        im.load()
+        assert im.mode == "RGB"
+        assert im.size == (128, 128)
+        assert im.format == "IM"
+
+
+def test_name_limit(tmp_path):
+    out = str(tmp_path / ("name_limit_test" * 7 + ".im"))
+    with Image.open(TEST_IM) as im:
+        im.save(out)
+    assert filecmp.cmp(out, "Tests/images/hopper_long_name.im")
+
+
+@pytest.mark.skipif(is_pypy(), reason="Requires CPython")
+def test_unclosed_file():
+    def open():
+        im = Image.open(TEST_IM)
+        im.load()
+
+    pytest.warns(ResourceWarning, open)
+
+
+def test_closed_file():
+    def open():
+        im = Image.open(TEST_IM)
+        im.load()
+        im.close()
+
+    pytest.warns(None, open)
+
+
+def test_context_manager():
+    def open():
         with Image.open(TEST_IM) as im:
             im.load()
-            self.assertEqual(im.mode, "RGB")
-            self.assertEqual(im.size, (128, 128))
-            self.assertEqual(im.format, "IM")
-
-    @unittest.skipIf(is_pypy(), "Requires CPython")
-    def test_unclosed_file(self):
-        def open():
-            im = Image.open(TEST_IM)
-            im.load()
 
-        pytest.warns(ResourceWarning, open)
+    pytest.warns(None, open)
 
-    def test_closed_file(self):
-        def open():
-            im = Image.open(TEST_IM)
-            im.load()
-            im.close()
 
-        pytest.warns(None, open)
+def test_tell():
+    # Arrange
+    with Image.open(TEST_IM) as im:
 
-    def test_context_manager(self):
-        def open():
-            with Image.open(TEST_IM) as im:
-                im.load()
+        # Act
+        frame = im.tell()
 
-        pytest.warns(None, open)
+    # Assert
+    assert frame == 0
 
-    def test_tell(self):
-        # Arrange
-        with Image.open(TEST_IM) as im:
 
-            # Act
-            frame = im.tell()
+def test_n_frames():
+    with Image.open(TEST_IM) as im:
+        assert im.n_frames == 1
+        assert not im.is_animated
 
-        # Assert
-        self.assertEqual(frame, 0)
 
-    def test_n_frames(self):
-        with Image.open(TEST_IM) as im:
-            self.assertEqual(im.n_frames, 1)
-            self.assertFalse(im.is_animated)
+def test_eoferror():
+    with Image.open(TEST_IM) as im:
+        n_frames = im.n_frames
 
-    def test_eoferror(self):
-        with Image.open(TEST_IM) as im:
-            n_frames = im.n_frames
+        # Test seeking past the last frame
+        with pytest.raises(EOFError):
+            im.seek(n_frames)
+        assert im.tell() < n_frames
+
+        # Test that seeking to the last frame does not raise an error
+        im.seek(n_frames - 1)
+
+
+def test_roundtrip(tmp_path):
+    def roundtrip(mode):
+        out = str(tmp_path / "temp.im")
+        im = hopper(mode)
+        im.save(out)
+        with Image.open(out) as reread:
+            assert_image_equal(reread, im)
 
-            # Test seeking past the last frame
-            self.assertRaises(EOFError, im.seek, n_frames)
-            self.assertLess(im.tell(), n_frames)
+    for mode in ["RGB", "P", "PA"]:
+        roundtrip(mode)
 
-            # Test that seeking to the last frame does not raise an error
-            im.seek(n_frames - 1)
 
-    def test_roundtrip(self):
-        for mode in ["RGB", "P", "PA"]:
-            out = self.tempfile("temp.im")
-            im = hopper(mode)
-            im.save(out)
-            with Image.open(out) as reread:
+def test_save_unsupported_mode(tmp_path):
+    out = str(tmp_path / "temp.im")
+    im = hopper("HSV")
+    with pytest.raises(ValueError):
+        im.save(out)
 
-                assert_image_equal(reread, im)
 
-    def test_save_unsupported_mode(self):
-        out = self.tempfile("temp.im")
-        im = hopper("HSV")
-        self.assertRaises(ValueError, im.save, out)
+def test_invalid_file():
+    invalid_file = "Tests/images/flower.jpg"
 
-    def test_invalid_file(self):
-        invalid_file = "Tests/images/flower.jpg"
+    with pytest.raises(SyntaxError):
+        ImImagePlugin.ImImageFile(invalid_file)
 
-        self.assertRaises(SyntaxError, ImImagePlugin.ImImageFile, invalid_file)
 
-    def test_number(self):
-        self.assertEqual(1.2, ImImagePlugin.number("1.2"))
+def test_number():
+    assert ImImagePlugin.number("1.2") == 1.2
diff --git a/src/PIL/ImImagePlugin.py b/src/PIL/ImImagePlugin.py
index 12c9237f082..8b03f35da8c 100644
--- a/src/PIL/ImImagePlugin.py
+++ b/src/PIL/ImImagePlugin.py
@@ -26,6 +26,7 @@
 #
 
 
+import os
 import re
 
 from . import Image, ImageFile, ImagePalette
@@ -347,7 +348,14 @@ def _save(im, fp, filename):
 
     fp.write(("Image type: %s image\r\n" % image_type).encode("ascii"))
     if filename:
-        fp.write(("Name: %s\r\n" % filename).encode("ascii"))
+        # Each line must be 100 characters or less,
+        # or: SyntaxError("not an IM file")
+        # 8 characters are used for "Name: " and "\r\n"
+        # Keep just the filename, ditch the potentially overlong path
+        name, ext = os.path.splitext(os.path.basename(filename))
+        name = "".join([name[: 92 - len(ext)], ext])
+
+        fp.write(("Name: %s\r\n" % name).encode("ascii"))
     fp.write(("Image size (x*y): %d*%d\r\n" % im.size).encode("ascii"))
     fp.write(("File size (no of images): %d\r\n" % frames).encode("ascii"))
     if im.mode in ["P", "PA"]: