Added symmetrical test for both SMono and SFlux .asJava and .asScala as a change on #69

(cherry picked from commit 5247c42)

Author: sinwe

src/test/scala/reactor/core/scala/publisher/SFluxTest.scala

@@ -2232,5 +2232,16 @@ class SFluxTest extends AnyFreeSpec with Matchers with TableDrivenPropertyChecks
     ".asJava should convert to java" in {
       SFlux.just(1, 2, 3).asJava() shouldBe a[reactor.core.publisher.Flux[_]]
     }
+
+    ".asScala and .asJava should be" - {
+      val jFlux: JFlux[Int] = JFlux.just(1, 2, 3)
+      "compile" in {
+        //noinspection ScalaUnusedSymbol
+        "val x: JFlux[Int] = jFlux.asScala.asJava()" should compile
+      }
+      "symmetrical" in {
+        jFlux.asScala.asJava() should be theSameInstanceAs jFlux
+      }
+    }
   }
 }

src/test/scala/reactor/core/scala/publisher/SMonoTest.scala

@@ -366,6 +366,17 @@ class SMonoTest extends AnyFreeSpec with Matchers with TestSupport with Idiomati
       JMono.just(randomValue).asScala shouldBe an[SMono[_]]
     }
 
+    ".asScala and .asJava should be" - {
+      val jMono: JMono[Long] = JMono.just(randomValue)
+      "compile" in {
+        //noinspection ScalaUnusedSymbol
+        "val x: JMono[Long] = jMono.asScala.asJava()" should compile
+      }
+      "symmetrical" in {
+        jMono.asScala.asJava() should be theSameInstanceAs jMono
+      }
+    }
+
     ".block" - {
       "should block the mono to get the value" in {
         just(randomValue).block() shouldBe randomValue