Fix unescaped backslash in theta label in model_variables.json

ogcore/model_variables.json

@@ -527,7 +527,7 @@
         "type": "array-like",
         "TPI dimensions": "",
         "SS dimensions": "J",
-        "label": "Replacement rate ($\theta_j$)",
+        "label": "Replacement rate ($\\theta_j$)",
         "toGDP_label": ""
     },
     "factor": {

tests/test_constants.py

@@ -0,0 +1,25 @@
+"""
+Tests of constants.py module and the label metadata loaded from
+model_variables.json.
+"""
+
+from ogcore import constants
+
+
+def test_labels_have_no_control_characters():
+    r"""
+    Guard against LaTeX label strings in model_variables.json being
+    written with a single backslash (e.g. "$\theta$"), which JSON parses
+    into a control character (a tab, in the case of "\t") and which then
+    fails to render in plots.  Backslashes must be escaped ("$\\theta$").
+    """
+    control_chars = set("\t\r\n\x08\x0c\x0b")
+    for label_map in (constants.VAR_LABELS, constants.ToGDP_LABELS):
+        for key, label in label_map.items():
+            assert isinstance(label, str)
+            bad = control_chars.intersection(label)
+            assert not bad, (
+                f"Label for {key!r} contains control character(s) "
+                f"{[c.encode('unicode_escape').decode() for c in bad]}: "
+                f"{label!r}. Escape backslashes in model_variables.json."
+            )