Bug Fix for the template render tool (#573)

src/uwtools/config/jinja2.py

@@ -170,7 +170,7 @@ def render(
     :param searchpath: Paths to search for extra templates.
     :param values_needed: Just report variables needed to render the template?
     :param dry_run: Run in dry-run mode?
-    :return: The rendered template, or None.
+    :return: The unrendered template if values_needed is True, the rendered template, or None.
     """
     _report(locals())
     values = _supplement_values(
@@ -180,11 +180,11 @@ def render(
     undeclared_variables = template.undeclared_variables
 
     # If a report of variables required to render the template was requested, make that report and
-    # then return.
+    # then return the unrendered template.
 
     if values_needed:
         _values_needed(undeclared_variables)
-        return None
+        return str(template)
 
     # Render the template. If there are missing values, report them and return an error to the
     # caller.

src/uwtools/tests/api/test_template.py

@@ -1,5 +1,6 @@
 # pylint: disable=missing-function-docstring,redefined-outer-name
 
+import logging
 import os
 from pathlib import Path
 from unittest.mock import patch
@@ -8,6 +9,8 @@
 
 from uwtools.api import template
 from uwtools.exceptions import UWTemplateRenderError
+from uwtools.logging import log
+from uwtools.tests.support import logged
 
 
 @fixture
@@ -25,6 +28,14 @@ def kwargs():
     }
 
 
+@fixture
+def template_file(tmp_path):
+    path = tmp_path / "template.jinja2"
+    with open(path, "w", encoding="utf-8") as f:
+        f.write("roses are {{roses_color}}, violets are {{violets_color}}")
+    return path
+
+
 def test_render(kwargs):
     with patch.object(template, "_render") as _render:
         template.render(**kwargs)
@@ -51,6 +62,13 @@ def test_render_to_str(kwargs):
         render.assert_called_once_with(**{**kwargs, "output_file": Path(os.devnull)})
 
 
+def test_render_values_needed(caplog, template_file):
+    log.setLevel(logging.INFO)
+    template.render(input_file=template_file, values_needed=True)
+    for var in ("roses_color", "violets_color"):
+        assert logged(caplog, f"  {var}")
+
+
 def test_translate():
     kwargs: dict = {
         "input_file": "path1",