Add more operator overloading to Observable and CompositeDisposable

src/main/kotlin/io/reactivex/rxjava3/kotlin/disposable.kt

@@ -10,10 +10,18 @@ operator fun CompositeDisposable.plusAssign(disposable: Disposable) {
     add(disposable)
 }
 
+
+/**
+ * disposable -= observable.subscribe()
+ */
+operator fun CompositeDisposable.minusAssign(disposable: Disposable) {
+    delete(disposable)
+}
+
 /**
  * Add the disposable to a CompositeDisposable.
  * @param compositeDisposable CompositeDisposable to add this disposable to
  * @return this instance
  */
 fun Disposable.addTo(compositeDisposable: CompositeDisposable): Disposable =
-        apply { compositeDisposable.add(this) }
+        apply { compositeDisposable += this }

src/main/kotlin/io/reactivex/rxjava3/kotlin/observable.kt

@@ -177,3 +177,11 @@ fun <A : Any, B : Any> Observable<Pair<A, B>>.toMultimap(): Single<MutableMap<A,
 @SchedulerSupport(SchedulerSupport.NONE)
 fun <T : Any> Iterable<ObservableSource<T>>.concatAll(): Observable<T> =
         Observable.concat(this)
+
+/**
+ * Merge multiple Observable by using plus operator
+ */
+@CheckReturnValue
+@SchedulerSupport(SchedulerSupport.NONE)
+operator fun <T: Any> Observable<T>.plus(other: Observable<T>): Observable<T> =
+        Observable.merge(this, other)

src/test/kotlin/io/reactivex/rxjava3/kotlin/ObservableTest.kt

@@ -268,7 +268,19 @@ class ObservableTest {
                 .concatAll()
                 .toList()
                 .subscribe { result ->
-                    Assert.assertEquals((0 until 30).toList(), result)
+                    assertEquals((0 until 30).toList(), result)
                 }
     }
+
+    @Test fun testMergeWithPlus() {
+        val output =
+            Observable.just(1, 2) +
+            Observable.just(3, 4) +
+            Observable.just(5, 6) +
+            Observable.just(7, 8) +
+            Observable.just(9, 10)
+        val result = mutableListOf<Int>()
+        output.subscribe { data -> result.add(data) }
+        assertEquals(result, (1..10).toMutableList())
+    }
 }

src/test/kotlin/io/reactivex/rxjava3/kotlin/SubscriptionTests.kt

@@ -2,28 +2,55 @@ package io.reactivex.rxjava3.kotlin
 
 import io.reactivex.rxjava3.core.Observable
 import io.reactivex.rxjava3.disposables.CompositeDisposable
+import org.junit.After
+import org.junit.Before
 import org.junit.Test
 import java.util.concurrent.TimeUnit
 
 class SubscriptionTest {
-    @Test fun testSubscriptionAddTo() {
-        val compositeSubscription = CompositeDisposable()
 
-        // Create an asynchronous subscription
-        // The delay ensures that we don't automatically unsubscribe because data finished emitting
-        val subscription = Observable.just("test")
-                .delay(100, TimeUnit.MILLISECONDS)
-                .subscribe()
+    // Create an asynchronous subscription
+    // The delay ensures that we don't automatically unsubscribe because data finished emitting
+    private val subscription = Observable.just("test")
+        .delay(100, TimeUnit.MILLISECONDS)
+        .subscribe()
 
+    private lateinit var compositeSubscription: CompositeDisposable
+
+    @Before
+    fun setUp() {
+        compositeSubscription = CompositeDisposable()
+    }
+
+    @After
+    fun tearDown() {
+        compositeSubscription.dispose()
+        assert(compositeSubscription.isDisposed)
+    }
+
+    @Test
+    fun testSubscriptionAddTo() {
         assert(!subscription.isDisposed)
 
         subscription.addTo(compositeSubscription)
 
         assert(compositeSubscription.size() > 0)
         assert(!subscription.isDisposed)
+    }
 
-        compositeSubscription.dispose()
+    @Test
+    fun testSubscriptionAddToWithPlusAssign() {
+        compositeSubscription += subscription
 
-        assert(compositeSubscription.isDisposed)
+        assert(compositeSubscription.size() > 0)
+    }
+
+    @Test
+    fun testSubscriptionDeleteWithMinusAssign() {
+        this.testSubscriptionAddToWithPlusAssign()
+
+        compositeSubscription -= subscription
+
+        assert(compositeSubscription.size() == 0)
     }
 }