Raise error if ImageMagick not found

Tests/test_imagegrab.py

@@ -5,11 +5,12 @@ import pytest
 
 from .helper import assert_image
 
-try:
-    from PIL import ImageGrab
+from PIL import ImageGrab
 
-    class TestImageGrab:
-        def test_grab(self):
+
+class TestImageGrab:
+    def test_grab(self):
+        if sys.platform in ["darwin", "win32"] or ImageGrab._has_imagemagick():
             for im in [
                 ImageGrab.grab(),
                 ImageGrab.grab(include_layered_windows=True),
@@ -19,50 +20,21 @@ try:
 
             im = ImageGrab.grab(bbox=(10, 20, 50, 80))
             assert_image(im, im.mode, (40, 60))
+        else:
+            pytest.raises(IOError, ImageGrab.grab)
 
-        def test_grabclipboard(self):
-            if sys.platform == "darwin":
-                subprocess.call(["screencapture", "-cx"])
-            else:
-                p = subprocess.Popen(
-                    ["powershell", "-command", "-"], stdin=subprocess.PIPE
-                )
-                p.stdin.write(
-                    b"""[Reflection.Assembly]::LoadWithPartialName("System.Drawing")
+    def test_grabclipboard(self):
+        if sys.platform == "darwin":
+            subprocess.call(["screencapture", "-cx"])
+        else:
+            p = subprocess.Popen(["powershell", "-command", "-"], stdin=subprocess.PIPE)
+            p.stdin.write(
+                b"""[Reflection.Assembly]::LoadWithPartialName("System.Drawing")
 [Reflection.Assembly]::LoadWithPartialName("System.Windows.Forms")
 $bmp = New-Object Drawing.Bitmap 200, 200
 [Windows.Forms.Clipboard]::SetImage($bmp)"""
-                )
-                p.communicate()
+            )
+            p.communicate()
 
-            im = ImageGrab.grabclipboard()
-            assert_image(im, im.mode, im.size)
-
-
-except ImportError:
-
-    class TestImageGrab:
-        @pytest.mark.skip(reason="ImageGrab ImportError")
-        def test_skip(self):
-            pass
-
-
-class TestImageGrabImport:
-    def test_import(self):
-        # Arrange
-        exception = None
-
-        # Act
-        try:
-            from PIL import ImageGrab
-
-            ImageGrab.__name__  # dummy to prevent Pyflakes warning
-        except Exception as e:
-            exception = e
-
-        # Assert
-        if sys.platform in ["win32", "darwin"]:
-            assert exception is None
-        else:
-            assert isinstance(exception, ImportError)
-            assert str(exception) == "ImageGrab is macOS and Windows only"
+        im = ImageGrab.grabclipboard()
+        assert_image(im, im.mode, im.size)

src/PIL/ImageGrab.py

@@ -23,6 +23,17 @@ import tempfile
 from . import Image
 
 
+def _has_imagemagick():
+    try:
+        with open(os.devnull, "wb") as devnull:
+            subprocess.check_call(["import", "--version"], stdout=devnull)
+        return True
+    except OSError:
+        # No ImageMagick
+        pass
+    return False
+
+
 def grab(bbox=None, include_layered_windows=False, all_screens=False):
     if sys.platform == "darwin":
         fh, filepath = tempfile.mkstemp(".png")
@@ -53,6 +64,8 @@ def grab(bbox=None, include_layered_windows=False, all_screens=False):
             left, top, right, bottom = bbox
             im = im.crop((left - x0, top - y0, right - x0, bottom - y0))
     else:
+        if not _has_imagemagick:
+            raise IOError("grab requires ImageMagick unless used on macOS or Windows")
         fh, filepath = tempfile.mkstemp(".png")
         os.close(fh)
         subprocess.call(["import", "-window", "root", filepath])