[SCALA-568] Added gatling simulation

for testing against a server with a steady load

scala-gatling/README.md

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+### Relevant Articles:
+- [Testing With Gatling Using Scala]()
+
+### Gatling Executions
+compile tests: `sbt test:compile`
+then run the simulation: `sbt 'Gatling/testOnly com.baeldung.gatling.PeakLoadSimulation'`

scala-gatling/src/test/scala/com/baeldung/gatling/ChainRequestsProvider.scala

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+package com.baeldung.gatling
+
+import io.gatling.core.Predef._
+import io.gatling.core.structure.ChainBuilder
+import io.gatling.http.Predef._
+import io.gatling.http.request.builder.HttpRequestBuilder
+
+object ChainRequestsProvider {
+
+  def simpleRequest(
+    requestName: String,
+    requestPath: String,
+    expectedResponseStatus: Int
+  ): ChainBuilder = {
+    val request: HttpRequestBuilder = http(requestName)
+      .get(requestPath)
+      .check(status.is(expectedResponseStatus))
+      .check(bodyString.optional.saveAs("sBodyString"))
+
+    exec(session => session.markAsSucceeded)
+      .exec(request)
+      .doIf(_.isFailed) {
+        exec { session =>
+          println("***Failure on [" + requestPath + "] endpoint:")
+          print("Gatling Session Data: ")
+          println(session.attributes.get("sBodyString"))
+          session
+        }
+      }
+  }
+}

scala-gatling/src/test/scala/com/baeldung/gatling/PeakLoadSimulation.scala

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+package com.baeldung.gatling
+
+import io.gatling.core.Predef.{details, _}
+import com.baeldung.gatling.ChainRequestsProvider.simpleRequest
+import com.baeldung.gatling.ScenariosProvider.getScenario
+
+class PeakLoadSimulation extends Simulation {
+
+  setUp(
+    getScenario(
+      "getExistingEndpoint",
+      simpleRequest("request_status_endpoint", "/health/status", 200),
+      50,
+      10,
+      60
+    ),
+    getScenario(
+      "nonExistingEndpoint",
+      simpleRequest("request_wrong_endpoint", "/health/status1", 200),
+      5,
+      10,
+      60
+    )
+  ).assertions(
+    details("request_status_endpoint").successfulRequests.percent.gt(99.99),
+    details("request_status_endpoint").responseTime.percentile4.lt(20),
+    details("request_status_endpoint").requestsPerSec.gt(40),
+    details("request_wrong_endpoint").successfulRequests.percent.lt(1),
+    details("request_wrong_endpoint").responseTime.percentile4.lt(20)
+  )
+}

scala-gatling/src/test/scala/com/baeldung/gatling/ScenariosProvider.scala

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+package com.baeldung.gatling
+
+import io.gatling.core.Predef._
+import io.gatling.core.structure.{ChainBuilder, PopulationBuilder}
+import io.gatling.http.Predef.http
+
+import scala.language.postfixOps
+
+object ScenariosProvider {
+
+  private val httpProtocol =
+    http.baseUrl("http://localhost:8080").disableCaching.disableFollowRedirect
+
+  def getScenario(
+    scenarioName: String,
+    request: ChainBuilder,
+    tps: Double,
+    rampUpSeconds: Int,
+    durationSeconds: Int
+  ): PopulationBuilder = {
+    scenario(scenarioName)
+      .exec(request)
+      .inject(
+        rampUsersPerSec(0).to(tps).during(rampUpSeconds),
+        constantUsersPerSec(tps)
+          .during(durationSeconds - rampUpSeconds - rampUpSeconds),
+        rampUsersPerSec(tps).to(0).during(rampUpSeconds)
+      )
+      .protocols(httpProtocol)
+  }
+}