test: Add tests for JWT token expiration and not before checks

test/header_test.dart

@@ -48,6 +48,70 @@ void main() {
           },
         );
       });
+
+      test('should be valid when exp is disabled', () {
+        final token =
+            JWT({'foo': 'bar'}).sign(hsKey, expiresIn: Duration(hours: -1));
+
+        expect(
+          JWT.verify(token, hsKey, checkExpiresIn: false).payload,
+          contains('foo'),
+        );
+      });
+    });
+
+    //----------------------//
+    //  Not Before (nbf)   //
+    //----------------------//
+    group('nbf', () {
+      test('should throw when token is not yet valid', () {
+        final notBefore = Duration(hours: 1);
+        final token = JWT({'foo': 'bar'}).sign(hsKey, notBefore: notBefore);
+
+        expect(
+          () => JWT.verify(token, hsKey),
+          throwsA(isA<JWTNotActiveException>()),
+        );
+      });
+
+      test('should be valid after nbf time', () {
+        final iat = DateTime(2023);
+        final nbf = iat.add(Duration(minutes: 30));
+
+        withClock(
+          Clock.fixed(DateTime(2023)),
+          () {
+            final token = JWT({'foo': 'bar'}).sign(
+              hsKey,
+              notBefore: Duration(minutes: 30),
+            );
+
+            fakeAsync((async) {
+              async.elapse(Duration(minutes: 45));
+              expect(
+                JWT.verify(token, hsKey).payload,
+                equals({
+                  'foo': 'bar',
+                  'iat': iat.millisecondsSinceEpoch ~/ 1000,
+                  'nbf': nbf.millisecondsSinceEpoch ~/ 1000,
+                }),
+              );
+            });
+          },
+        );
+      });
+
+      test('should be valid when nbf check is disabled', () {
+        final token = JWT({'foo': 'bar'}).sign(
+          hsKey,
+          notBefore: Duration(hours: 1),
+        );
+
+        expect(
+          JWT.verify(token, hsKey, checkNotBefore: false).payload,
+          contains('foo'),
+        );
+      });
     });
   });
 }