More unit tests

UpsilonTests/StandardLibraryTests/BasicFunctionsTests.cs

@@ -1,3 +1,4 @@
+using System;
 using Upsilon.Evaluator;
 using Xunit;
 
@@ -10,9 +11,18 @@ namespace UpsilonTests.StandardLibraryTests
         }
 
         [Fact]
-        public void Assert()
+        public void AssertTest()
         {
             new Script("assert(true)", BoundScope, StaticScope).Evaluate();
+            Assert.Throws<Exception>(() => new Script("assert(false)", BoundScope, StaticScope).Evaluate());
+        }
+
+        [Fact]
+        public void Error()
+        {
+            var e = Assert.Throws<Exception>(() =>
+                new Script(@"error(""test_error"")", BoundScope, StaticScope).Evaluate());
+            Assert.Equal("test_error", e.Message);
         }
 
     }