Fix tracer parsing function to properly handle variables

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    changed:
+    - Fixed tracer parsing function. It was not properly handling variables whose names are substrings of other variables.

policyengine_api/services/tracer_analysis_service.py

@@ -112,8 +112,10 @@ def _parse_tracer_output(self, tracer_output, target_variable):
         # Create a regex pattern to match the exact variable name
         # This will match the variable name followed by optional whitespace,
         # then optional angle brackets with any content, then optional whitespace
-        pattern = rf"^(\s*)({re.escape(target_variable)})\s*(?:<[^>]*>)?\s*"
 
+        pattern = (
+            rf"^(\s*)({re.escape(target_variable)})(?!\w)\s*(?:<[^>]*>)?\s*"
+        )
         for line in tracer_output:
             # Count leading spaces to determine indentation level
             indent = len(line) - len(line.strip())

tests/fixtures/services/tracer_analysis_service.py

@@ -21,4 +21,8 @@
 
 spliced_valid_tracer_output_leaf_variable = valid_tracer_output[8:]
 
+spliced_valid_tracer_output_for_variable_that_is_substring_of_another = (
+    valid_tracer_output[7:8]
+)
+
 empty_tracer = []

tests/unit/services/test_tracer_analysis_service.py

@@ -130,3 +130,21 @@ def test_tracer_output_for_leaf_variable():
     # Then: It should return only leaf variable since it has no children
     expected_output = spliced_valid_tracer_output_leaf_variable
     assert result == expected_output
+
+
+def test_tracer_output_for_variable_that_is_substring_of_another():
+    # Given: A tracer output with variables where one is a substring of another
+    # and the target variable that's a substring of another variable
+    target_variable = "snap_net_income"
+
+    # When: Extracting the segment for this variable
+    result = test_service._parse_tracer_output(
+        valid_tracer_output, target_variable
+    )
+
+    # Then: It should return only the exact match for "snap_net_income", not "snap_net_income_fpg_ratio"
+
+    expected_output = (
+        spliced_valid_tracer_output_for_variable_that_is_substring_of_another
+    )
+    assert result == expected_output