Improve error when checksum dict has no entry for a file

When the dict didn't contain the filename EB will crash with
> Invalid checksum spec 'None', should be a string (MD5) or 2-tuple (type, value).

This will now raise a more descriptive error

easybuild/tools/filetools.py

@@ -1265,14 +1265,11 @@ def verify_checksum(path, checksums):
 
     for checksum in checksums:
         if isinstance(checksum, dict):
-            if filename in checksum:
+            try:
                 # Set this to a string-type checksum
                 checksum = checksum[filename]
-            elif build_option('enforce_checksums'):
-                raise EasyBuildError("Missing checksum for %s", filename)
-            else:
-                # Set to None and allow to fail elsewhere
-                checksum = None
+            except KeyError:
+                raise EasyBuildError("Missing checksum for %s in %s", filename, checksum)
 
         if isinstance(checksum, string_type):
             # if no checksum type is specified, it is assumed to be MD5 (32 characters) or SHA256 (64 characters)

test/framework/filetools.py

@@ -348,6 +348,14 @@ def test_checksums(self):
         alt_checksums = ('7167b64b1ca062b9674ffef46f9325db7167b64b1ca062b9674ffef46f9325db', broken_checksums['sha256'])
         self.assertFalse(ft.verify_checksum(fp, alt_checksums))
 
+        # Check dictionary
+        alt_checksums = (known_checksums['sha256'],)
+        self.assertTrue(ft.verify_checksum(fp, {os.path.basename(fp): known_checksums['sha256']}))
+        faulty_dict = {'wrong-name': known_checksums['sha256']}
+        self.assertErrorRegex(EasyBuildError,
+                              "Missing checksum for " + os.path.basename(fp) + " in .*wrong-name.*",
+                              ft.verify_checksum, fp, faulty_dict)
+
         # check whether missing checksums are enforced
         build_options = {
             'enforce_checksums': True,
@@ -362,6 +370,8 @@ def test_checksums(self):
         for checksum in [known_checksums[x] for x in ('md5', 'sha256')]:
             dict_checksum = {os.path.basename(fp): checksum, 'foo': 'baa'}
             self.assertTrue(ft.verify_checksum(fp, dict_checksum))
+            del dict_checksum[os.path.basename(fp)]
+            self.assertErrorRegex(EasyBuildError, "Missing checksum for", ft.verify_checksum, fp, dict_checksum)
 
     def test_common_path_prefix(self):
         """Test get common path prefix for a list of paths."""