Add tests for ws connection metric

src/main/kotlin/org/codefreak/cloud/companion/WebsocketConnectionMetricAdvice.kt

@@ -57,4 +57,4 @@ class WebsocketConnectionMetricAdvice(
         } while (!connectionCounter.compareAndSet(currentCount, newCount))
         log.debug("Client disconnected! New connection count: $newCount")
     }
-}
+}

src/test/kotlin/org/codefreak/cloud/companion/WebsocketConnectionMetricAdviceTest.kt

@@ -0,0 +1,40 @@
+package org.codefreak.cloud.companion
+
+import io.micrometer.core.instrument.Gauge
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry
+import org.aspectj.lang.ProceedingJoinPoint
+import org.hamcrest.CoreMatchers.`is`
+import org.hamcrest.MatcherAssert.assertThat
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import org.mockito.Mockito
+import org.mockito.Mockito.`when`
+import org.mockito.Mockito.any
+import reactor.core.publisher.Mono
+import reactor.test.StepVerifier
+
+internal class WebsocketConnectionMetricAdviceTest {
+
+    private lateinit var connectionMetricAdvice: WebsocketConnectionMetricAdvice
+    private lateinit var gauge: Gauge
+
+    @BeforeEach
+    fun beforeEach() {
+        val meterRegistry = SimpleMeterRegistry()
+        connectionMetricAdvice = WebsocketConnectionMetricAdvice(meterRegistry)
+        gauge = meterRegistry.get("http.websocket.connections").gauge()
+    }
+
+    @Test
+    fun testCountsUpAndDown() {
+        val pjp = Mockito.mock(ProceedingJoinPoint::class.java)
+        `when`(pjp.proceed(any())).thenReturn(Mono.just("1"))
+        val wrappedMono = connectionMetricAdvice.onHandle(pjp)
+
+        assertThat(gauge.value(), `is`(.0))
+        StepVerifier.create(wrappedMono)
+            .assertNext { assertThat(gauge.value(), `is`(1.0)) }
+            .verifyComplete()
+        assertThat(gauge.value(), `is`(.0))
+    }
+}