bugfix: show dot after namespaces in spack find -N (spack#11945)

- Namepsaces were shown without dots after the new format strings were
  added.

- Add a test for `spack find` to ensure that find -N shows the right
  output.

lib/spack/spack/cmd/__init__.py

@@ -264,7 +264,7 @@ def get_arg(name, default=None):
         hashes = True
         hlen = None
 
-    nfmt = '{namespace}{name}' if namespace else '{name}'
+    nfmt = '{namespace}.{name}' if namespace else '{name}'
     ffmt = ''
     if full_compiler or flags:
         ffmt += '{%compiler.name}'

lib/spack/spack/test/cmd/find.py

@@ -7,9 +7,13 @@
 
 import pytest
 import spack.cmd.find
+from spack.main import SpackCommand
 from spack.util.pattern import Bunch
 
 
+find = SpackCommand('find')
+
+
 @pytest.fixture(scope='module')
 def parser():
     """Returns the parser for the module command"""
@@ -98,3 +102,12 @@ def test_tag2_tag3(parser, specs):
     spack.cmd.find.find(parser, args)
 
     assert len(specs) == 0
+
+
+@pytest.mark.db
+def test_namespaces_shown_correctly(database):
+    out = find()
+    assert 'builtin.mock.zmpi' not in out
+
+    out = find('--namespace')
+    assert 'builtin.mock.zmpi' in out