fix: 🐛 correct error message in UnitSystem#convert

Author: alanhussey

src/UnitSystem/UnitSystem.js

@@ -78,7 +78,9 @@ class UnitSystem {
       );
     }
     if (!(endUnit instanceof Unit)) {
-      throw new TypeError('Expected a Unit, got "{"name":"inch"}" instead');
+      throw new TypeError(
+        `Expected a Unit, got "${JSON.stringify(endUnit)}" instead`
+      );
     }
     if (measurement.unit === endUnit) {
       return measurement;

src/UnitSystem/UnitSystem.test.js

@@ -145,7 +145,7 @@ describe(UnitSystem, () => {
       expect(() => {
         system.convert(new Measurement(12, inch), { name: 'foot' });
       }).toThrowError(
-        new TypeError('Expected a Unit, got "{"name":"inch"}" instead')
+        new TypeError('Expected a Unit, got "{"name":"foot"}" instead')
       );
     });
   });