Remove literal text checks from predicate position helpers

Co-authored-by: Codex <noreply@openai.com>

Author: rcosta358

liquidjava-verifier/src/test/java/liquidjava/api/tests/TestDeclarationPositions.java

@@ -61,20 +61,27 @@ private static void assertDeclarations(String file, String title, String... pred
     private static void assertPredicatePosition(SourcePosition position, Path file, String source, String predicate)
             throws IOException {
         assertNotNull(position, "Missing refinement declaration position");
-        int start = source.indexOf("\"" + predicate + "\"") + 1;
-        assertTrue(start > 0, "Predicate not found in fixture: " + predicate);
-        assertEquals(start, position.getSourceStart());
-        assertEquals(start + predicate.length() - 1, position.getSourceEnd());
+        assertTrue(position.isValidPosition(), "Invalid refinement declaration position");
+        int start = position.getSourceStart();
+        int end = position.getSourceEnd();
+        assertTrue(start > 0 && end >= start && end + 1 < source.length(), "Declaration outside source bounds");
+        assertEquals(predicate.length(), end - start + 1);
+        assertEquals('"', source.charAt(start - 1));
+        assertEquals('"', source.charAt(end + 1));
         assertEquals(file, position.getFile().toPath().toRealPath());
     }
 
     private static void assertPredicateUnderline(LJError error, String predicate) {
         String output = error.toString().replaceAll("\u001B\\[[;\\d]*m", "");
-        String heading = "--> Refinement declared here:\n";
-        assertTrue(output.contains(heading), "Missing refinement declaration snippet");
-        String snippet = output.substring(output.indexOf(heading) + heading.length());
-        String indent = " ".repeat(error.getDeclarationPosition().getColumn() - 1);
+        SourcePosition position = error.getDeclarationPosition();
+        List<String> lines = output.lines().toList();
+        String sourceLine = position.getLine() + " | ";
+        String indent = " ".repeat(position.getColumn() - 1);
         String underline = "^".repeat(predicate.length());
-        assertTrue(snippet.contains(indent + underline + "\n"), snippet);
+        for (int i = 0; i + 1 < lines.size(); i++) {
+            if (lines.get(i).stripLeading().startsWith(sourceLine) && lines.get(i + 1).endsWith(indent + underline))
+                return;
+        }
+        fail("Missing predicate underline:\n" + output);
     }
 }