More test for formula solver

lib/formula_evaluator.dart

@@ -415,6 +415,7 @@ Number functionSolver(
 
     while (iter < maxNewtonIters) {
       final Number y = f(x);
+      print( "iter: $iter x: $x y: $y");
       if (y == 0 || y.abs() <= maxDelta) {
         return x;
       }
@@ -446,9 +447,16 @@ Number functionSolver(
 
   try {
     return searchNewton();
-  } catch (e) {
-    var approx = searchApproximately(hint, hint + step);
-    return binarySearch(approx[0], approx[1]);
+  } catch (e1) {
+    try {
+      var approx = searchApproximately(hint, hint + step);
+      return binarySearch(approx[0], approx[1]);
+    }
+    catch( e2 ){
+      errorHandler.notify(e1);
+      errorHandler.notify(e2);
+      throw NoSolutionException("Failed to find a root using both Newton-Raphson and approximate search: $e1 -- $e2");
+    }
   }
 
 }

test/formula_solver_test.dart

@@ -1,7 +1,8 @@
+import 'dart:math' as Math;
+
 import 'package:d4rt_formulas/formula_evaluator.dart';
 import 'package:d4rt_formulas/formula_models.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'dart:math' as Math;
 
 
 void main() {
@@ -22,6 +23,20 @@ void main() {
       expect( solution, closeTo(5, 1e-10));
     });
 
+
+    test("Solve x formula", () {
+      final formula = Formula(
+        name: 'Test x',
+        input: [
+          VariableSpec(name: 'x', unit: 'scalar'),
+        ],
+        output: VariableSpec(name: 'y', unit: 'scalar'),
+        d4rtCode: 'y = x;',
+      );
+
+      var solution = formulaSolver(formula, "x", {"y": 123456789}, maxDelta: 1e-10);
+      expect(solution, closeTo(123456789, 1e-10));
+    });
   });
 
   group('Native functions', () {
@@ -75,5 +90,4 @@ void main() {
       expect(root, closeTo(Math.log(2), 0.01));
     });
   });
-
 }