fix: add render_percent() method for app handler

src/wuttjamaican/app.py

@@ -772,6 +772,22 @@ class AppHandler:
         """
         return simple_error(error)
 
+    def render_percent(self, value, decimals=2):
+        """
+        Return a human-friendly display string for the given
+        percentage value, e.g. ``23.45139`` becomes ``"23.45 %"``.
+
+        :param value: The value to be rendered.
+
+        :returns: Display string for the percentage value.
+        """
+        if value is None:
+            return ""
+        fmt = f'{{:0.{decimals}f}} %'
+        if value < 0:
+            return f'({fmt.format(-value)})'
+        return fmt.format(value)
+
     def render_quantity(self, value, empty_zero=False):
         """
         Return a human-friendly display string for the given quantity

tests/test_app.py

@@ -491,6 +491,22 @@ app_title = WuttaTest
             result = self.app.render_error(error)
         self.assertEqual(result, "RuntimeError")
 
+    def test_render_percent(self):
+
+        # null
+        self.assertEqual(self.app.render_percent(None), "")
+
+        # typical
+        self.assertEqual(self.app.render_percent(12.3419), '12.34 %')
+
+        # more decimal places
+        self.assertEqual(self.app.render_percent(12.3419, decimals=3), '12.342 %')
+        self.assertEqual(self.app.render_percent(12.3419, decimals=4), '12.3419 %')
+
+        # negative
+        self.assertEqual(self.app.render_percent(-12.3419), '(12.34 %)')
+        self.assertEqual(self.app.render_percent(-12.3419, decimals=3), '(12.342 %)')
+
     def test_render_quantity(self):
 
         # null