feat(tests): Only allow unittests to run in checked mode.

Author: jbdeboer

test/_specs.dart

@@ -64,7 +64,7 @@ class Expect {
   toContain(expected) => unit.expect(actual, unit.contains(expected));
   toBe(expected) => unit.expect(actual,
       unit.predicate((actual) => identical(expected, actual), '$expected'));
-  toThrow(exception) => unit.expect(actual, unit.throwsA(unit.contains(exception)));
+  toThrow([exception]) => unit.expect(actual, exception == null ? unit.throws : unit.throwsA(unit.contains(exception)));
   toBeFalsy() => unit.expect(actual, (v) => v == null ? true : v is bool ? v == false : !(v is Object));
   toBeTruthy() => unit.expect(actual, (v) => v is bool ? v == true : v is Object);
   toBeDefined() => unit.expect(actual, (v) => v is Object);

test/angular_spec.dart

@@ -1,6 +1,14 @@
 import '_specs.dart';
 
 main() {
+  describe('angular.dart unittests', () {
+    it('should run in checked moded only', () {
+      expect(() {
+        String s = 6;
+      }).toThrow();
+    });
+  });
+
   describe('relaxFnApply', () {
     it('should work with 6 arguments', () {
       var sixArgs = [1, 1, 2, 3, 5, 8];