fix(typo)

Author: ctranxuan

Part 4 - Concurrency/2. Testing Rx.md

@@ -176,7 +176,7 @@ This is useful for testing small, self-contained pieces of Rx code, such as cust
 
 ### TestSubscriber
 
-In the test above, we manually collected the values emitted and compared them against what we expected. This process is common enough in tests that Rx comes packaged with `TestScubscriber`, which will do that for us. Its event handlers will collect every notification received and make them available for us to inspect. With `TestSubscriber` our [previous test becomes](/tests/java/itrx/chapter4/testing/TestSubscriberExample.java):
+In the test above, we manually collected the values emitted and compared them against what we expected. This process is common enough in tests that Rx comes packaged with `TestSubscriber`, which will do that for us. Its event handlers will collect every notification received and make them available for us to inspect. With `TestSubscriber` our [previous test becomes](/tests/java/itrx/chapter4/testing/TestSubscriberExample.java):
 
 ```java
 @Test