Add test from #612 for usage error Argument format

Adds a test that ensures that when an Argument is formatted into a usage
error, its metavar is used, not its name.
Additionally, repair testsuite to expect the new behavior.

click/core.py

@@ -1753,7 +1753,7 @@ def get_usage_pieces(self, ctx):
         return [self.make_metavar()]
 
     def get_error_hint(self, ctx):
-        return self.make_metavar()
+        return '"%s"' % self.make_metavar()
 
     def add_to_parser(self, parser, ctx):
         parser.add_argument(dest=self.name, nargs=self.nargs,

tests/test_arguments.py

@@ -188,7 +188,7 @@ def cmd2(arg):
 
     result = runner.invoke(cmd2, [])
     assert result.exit_code == 2
-    assert 'Missing argument "arg"' in result.output
+    assert 'Missing argument "ARG..."' in result.output
 
 
 def test_missing_arg(runner):
@@ -199,7 +199,7 @@ def cmd(arg):
 
     result = runner.invoke(cmd, [])
     assert result.exit_code == 2
-    assert 'Missing argument "arg".' in result.output
+    assert 'Missing argument "ARG".' in result.output
 
 
 def test_implicit_non_required(runner):

tests/test_formatting.py

@@ -159,7 +159,27 @@ def cmd(arg):
         'Usage: cmd [OPTIONS] ARG',
         'Try "cmd --help" for help.',
         '',
-        'Error: Missing argument "arg".'
+        'Error: Missing argument "ARG".'
+    ]
+
+
+def test_formatting_usage_error_metavar(runner):
+    """
+    :author: @r-m-n
+    Including attribution to #612
+    """
+    @click.command()
+    @click.argument('arg', metavar='metavar')
+    def cmd(arg):
+        pass
+
+    result = runner.invoke(cmd, [])
+    assert result.exit_code == 2
+    assert result.output.splitlines() == [
+        'Usage: cmd [OPTIONS] metavar',
+        'Try "cmd --help" for help.',
+        '',
+        'Error: Missing argument "metavar".'
     ]
 
 
@@ -179,7 +199,7 @@ def foo(bar):
         'Usage: cmd foo [OPTIONS] BAR',
         'Try "cmd foo --help" for help.',
         '',
-        'Error: Missing argument "bar".'
+        'Error: Missing argument "BAR".'
     ]
 
 
@@ -194,7 +214,7 @@ def cmd(arg):
     assert result.output.splitlines() == [
         'Usage: cmd [OPTIONS] ARG',
         '',
-        'Error: Missing argument "arg".'
+        'Error: Missing argument "ARG".'
     ]
 
 
@@ -210,5 +230,5 @@ def cmd(arg):
         'Usage: cmd [OPTIONS] ARG',
         'Try "cmd --man" for help.',
         '',
-        'Error: Missing argument "arg".'
+        'Error: Missing argument "ARG".'
     ]