MINOR: Reduce build time by gating test coverage plugins behind a flag (

apache#8899)

Most builds don't require test coverage output, so it's wasteful
to spend cycles tracking coverage information for each method
invoked.

I ran a quick test in a fast desktop machine, the absolute
difference will be larger in a slower machine. The tests were
executed after `./gradlew clean` and with a gradle daemon
that was started just before the test (and mildly warmed up
by running `./gradlew clean` again).

`./gradlew unitTest --continue --profile`:
* With coverage enabled: 6m32s
* With coverage disabled: 5m47s

I ran the same test twice and the results were within 2s of
each other, so reasonably consistent.

16% reduction in the time taken to run the unit tests is a
reasonable gain with little downside, so I think this is a
good change.

Reviewers: Manikumar Reddy <[email protected]>

README.md

@@ -60,11 +60,11 @@ See [Test Retry Gradle Plugin](https://github.com/gradle/test-retry-gradle-plugi
 ### Generating test coverage reports ###
 Generate coverage reports for the whole project:
 
-    ./gradlew reportCoverage
+    ./gradlew reportCoverage -PenableTestCoverage=true
 
 Generate coverage for a single module, i.e.: 
 
-    ./gradlew clients:reportCoverage
+    ./gradlew clients:reportCoverage -PenableTestCoverage=true
 
 ### Building a binary release gzipped tar ball ###
     ./gradlew clean releaseTarGz
@@ -208,6 +208,9 @@ The following options should be set with a `-P` switch, for example `./gradlew -
 * `xmlSpotBugsReport`: enable XML reports for spotBugs. This also disables HTML reports as only one can be enabled at a time.
 * `maxTestRetries`: the maximum number of retries for a failing test case.
 * `maxTestRetryFailures`: maximum number of test failures before retrying is disabled for subsequent tests.
+* `enableTestCoverage`: enables test coverage plugins and tasks, including bytecode enhancement of classes required to track said
+coverage. Note that this introduces some overhead when running tests and hence why it's disabled by default (the overhead
+varies, but 15-20% is a reasonable estimate).
 
 ### Dependency Analysis ###
 

build.gradle

@@ -115,6 +115,8 @@ ext {
 
   userTestLoggingEvents = project.hasProperty("testLoggingEvents") ? Arrays.asList(testLoggingEvents.split(",")) : null
 
+  userEnableTestCoverage = project.hasProperty("enableTestCoverage") ? enableTestCoverage : false
+
   generatedDocsDir = new File("${project.rootDir}/docs/generated")
 
   commitId = project.hasProperty('commitId') ? commitId : null
@@ -552,28 +554,33 @@ subprojects {
 
   // Ignore core since its a scala project
   if (it.path != ':core') {
-    apply plugin: "jacoco"
-
-    jacoco {
-      toolVersion = versions.jacoco
-    }
-
-    // NOTE: Jacoco Gradle plugin does not support "offline instrumentation" this means that classes mocked by PowerMock
-    // may report 0 coverage, since the source was modified after initial instrumentation.
-    // See https://github.com/jacoco/jacoco/issues/51
-    jacocoTestReport {
-      dependsOn tasks.test
-      sourceSets sourceSets.main
-      reports {
-        html.enabled = true
-        xml.enabled = true
-        csv.enabled = false
+    if (userEnableTestCoverage) {
+      apply plugin: "jacoco"
+
+      jacoco {
+        toolVersion = versions.jacoco
       }
+
+      // NOTE: Jacoco Gradle plugin does not support "offline instrumentation" this means that classes mocked by PowerMock
+      // may report 0 coverage, since the source was modified after initial instrumentation.
+      // See https://github.com/jacoco/jacoco/issues/51
+      jacocoTestReport {
+        dependsOn tasks.test
+        sourceSets sourceSets.main
+        reports {
+          html.enabled = true
+          xml.enabled = true
+          csv.enabled = false
+        }
+      }
+
     }
   }
 
-  def coverageGen = it.path == ':core' ? 'reportScoverage' : 'jacocoTestReport'
-  task reportCoverage(dependsOn: [coverageGen])
+  if (userEnableTestCoverage) {
+    def coverageGen = it.path == ':core' ? 'reportScoverage' : 'jacocoTestReport'
+    task reportCoverage(dependsOn: [coverageGen])
+  }
 
   task determineCommitId {
     def takeFromHash = 16
@@ -640,30 +647,34 @@ def checkstyleConfigProperties(configFileName) {
 }
 
 // Aggregates all jacoco results into the root project directory
-task jacocoRootReport(type: org.gradle.testing.jacoco.tasks.JacocoReport) {
-  def javaProjects = subprojects.findAll { it.path != ':core' }
+if (userEnableTestCoverage) {
+  task jacocoRootReport(type: org.gradle.testing.jacoco.tasks.JacocoReport) {
+    def javaProjects = subprojects.findAll { it.path != ':core' }
 
-  description = 'Generates an aggregate report from all subprojects'
-  dependsOn(javaProjects.test)
+    description = 'Generates an aggregate report from all subprojects'
+    dependsOn(javaProjects.test)
 
-  additionalSourceDirs.from = javaProjects.sourceSets.main.allSource.srcDirs
-  sourceDirectories.from = javaProjects.sourceSets.main.allSource.srcDirs
-  classDirectories.from = javaProjects.sourceSets.main.output
-  executionData.from = javaProjects.jacocoTestReport.executionData
+    additionalSourceDirs.from = javaProjects.sourceSets.main.allSource.srcDirs
+    sourceDirectories.from = javaProjects.sourceSets.main.allSource.srcDirs
+    classDirectories.from = javaProjects.sourceSets.main.output
+    executionData.from = javaProjects.jacocoTestReport.executionData
 
-  reports {
-    html.enabled = true
-    xml.enabled = true
-  }
+    reports {
+      html.enabled = true
+      xml.enabled = true
+    }
 
-  // workaround to ignore projects that don't have any tests at all
-  onlyIf = { true }
-  doFirst {
-    executionData = files(executionData.findAll { it.exists() })
+    // workaround to ignore projects that don't have any tests at all
+    onlyIf = { true }
+    doFirst {
+      executionData = files(executionData.findAll { it.exists() })
+    }
   }
 }
 
-task reportCoverage(dependsOn: ['jacocoRootReport', 'core:reportCoverage'])
+if (userEnableTestCoverage) {
+  task reportCoverage(dependsOn: ['jacocoRootReport', 'core:reportCoverage'])
+}
 
 def connectPkgs = [
     'connect:api',
@@ -684,7 +695,8 @@ project(':core') {
   println "Building project 'core' with Scala version ${versions.scala}"
 
   apply plugin: 'scala'
-  apply plugin: "org.scoverage"
+  if (userEnableTestCoverage)
+    apply plugin: "org.scoverage"
   archivesBaseName = "kafka_${versions.baseScala}"
 
   dependencies {
@@ -736,11 +748,13 @@ project(':core') {
     testCompile libs.jfreechart
   }
 
-  scoverage {
-    scoverageVersion = versions.scoverage
-    reportDir = file("${rootProject.buildDir}/scoverage")
-    highlighting = false
-    minimumRate = 0.0
+  if (userEnableTestCoverage) {
+    scoverage {
+      scoverageVersion = versions.scoverage
+      reportDir = file("${rootProject.buildDir}/scoverage")
+      highlighting = false
+      minimumRate = 0.0
+    }
   }
 
   configurations {