test: Extend scheduler tests and add coverage reports (#5)

---------
Signed-off-by: starry-shivam <[email protected]>

.github/workflows/tests.yml

@@ -12,15 +12,15 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
-    - name: set up JDK 21
-      uses: actions/setup-java@v3
-      with:
-        java-version: '21'
-        distribution: 'temurin'
-        cache: gradle
+      - uses: actions/checkout@v3
+      - name: set up JDK 21
+        uses: actions/setup-java@v3
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+          cache: gradle
 
-    - name: Grant execute permission for gradlew
-      run: chmod +x gradlew
-    - name: Run tests with gradle
-      run: ./gradlew test --stacktrace
+      - name: Grant execute permission for gradlew
+        run: chmod +x gradlew
+      - name: Run tests with gradle
+        run: ./gradlew test --stacktrace

README.md

@@ -13,7 +13,9 @@
   <a href="https://www.repostatus.org/#active"><img src="https://www.repostatus.org/badges/latest/active.svg" alt="Project Status: Active – The project has reached a stable, usable state and is being actively developed." /></a>
 </p>
 
-**KtScheduler** is a lightweight task/job scheduling library for Kotlin, powered by Kotlin coroutines! The design of this library is inspired by the [APScheduler](https://github.com/agronholm/apscheduler) library for Python, while keeping things simple and easy to use.
+**KtScheduler** is a lightweight task/job scheduling library for Kotlin, powered by Kotlin coroutines! The design of
+this library is inspired by the [APScheduler](https://github.com/agronholm/apscheduler) library for Python, while
+keeping things simple and easy to use.
 
 ------
 
@@ -66,7 +68,8 @@ scheduler.idle()
 
 #### Triggers
 
-Triggers determine when and at what frequency a particular job should be executed. KtScheduler provides four types of triggers:
+Triggers determine when and at what frequency a particular job should be executed. KtScheduler provides four types of
+triggers:
 
 1. `CronTrigger` - A trigger that determines the next run time based on the specified days of the week and time.
 
@@ -131,7 +134,8 @@ class WeekendTrigger(private val time: LocalTime) : Trigger {
 
 #### Listening for Job Events
 
-You can listen for job events such as completion or failure due to errors by attaching a `JobEventListener` to the `KtScheduler`. Here's an example:
+You can listen for job events such as completion or failure due to errors by attaching a `JobEventListener` to
+the `KtScheduler`. Here's an example:
 
 ```kotlin
 import dev.starry.ktscheduler.event.JobEvent
@@ -150,21 +154,26 @@ class MyEventListener : JobEventListener {
 val eventListener = MyEventListener()
 scheduler.addEventListener(eventListener)
 ```
+
 ------
 
-#### Contributing 🫶
+### Contributing 🫶
 
-Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change, or feel free to tackle any of the open issues present at the moment. If you're doing the latter, please leave a comment on the issue you want to contribute to before starting to work on it.
+Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change, or
+feel free to tackle any of the open issues present at the moment. If you're doing the latter, please leave a comment on
+the issue you want to contribute to before starting to work on it.
 
 ------
 
-#### Supporting ❤️
+### Supporting ❤️
 
-If you found this library helpful, you can support me by giving a small tip via [GitHub Sponsors](https://github.com/sponsors/starry-shivam) and joining the list of stargazers 🌟
+If you found this library helpful, you can support me by giving a small tip
+via [GitHub Sponsors](https://github.com/sponsors/starry-shivam) and joining the list of stargazers 🌟
 
 ------
 
-#### License ©️
+### License ©️
+
 ```
 Copyright [2024 - Present] starry-shivam
 

build.gradle.kts

@@ -1,5 +1,6 @@
 plugins {
     kotlin("jvm") version "2.0.0"
+    id("org.jetbrains.kotlinx.kover") version "0.8.1"
     `maven-publish`
 }
 
@@ -21,13 +22,18 @@ dependencies {
     testImplementation("org.jetbrains.kotlin:kotlin-test-junit:2.0.0")
 }
 
+kover {
+    reports {
+        verify { rule { minBound(70) } }
+    }
+}
 
 publishing {
     publications {
         register("mavenJava", MavenPublication::class) {
-            groupId = "dev.starry.ktscheduler"
+            groupId = group.toString()
             artifactId = "ktscheduler"
-            version = "1.0.0"
+            version = version.toString()
             from(components["java"])
         }
     }

src/main/kotlin/scheduler/KtScheduler.kt

@@ -58,10 +58,6 @@ class KtScheduler(
         private val logger = Logger.getLogger(TAG)
     }
 
-    // The coroutine scope with a SupervisorJob to prevent cancellation of all jobs
-    // if one of them fails.
-    private val coroutineScope = CoroutineScope(Dispatchers.Default + SupervisorJob())
-
     // The list of event listeners attached to the scheduler.
     private val eventListeners = mutableListOf<JobEventListener>()
 
@@ -77,14 +73,26 @@ class KtScheduler(
     // The tick interval in milliseconds.
     private val tickInterval = 100L
 
+    // The coroutine scope with a SupervisorJob to prevent cancellation of all jobs
+    // if one of them fails.
+    private lateinit var coroutineScope: CoroutineScope
+
     /**
      * Starts the scheduler.
      *
      * The scheduler will run in a coroutine and continuously process due jobs
      * at the specified tick interval unless it is paused or shut down.
+     *
+     * @throws IllegalStateException If the scheduler is already running.
      */
     override fun start() {
+        // Check if the scheduler is already running.
+        if (::coroutineScope.isInitialized && coroutineScope.isActive) {
+            throw IllegalStateException("Scheduler is already running")
+        }
+        // Start the scheduler.
         logger.info("Starting scheduler")
+        coroutineScope = createCoroutineScope()
         coroutineScope.launch {
             while (isActive) {
                 if (!isPaused) {
@@ -231,6 +239,9 @@ class KtScheduler(
         eventListeners.add(listener)
     }
 
+    // Creates a new coroutine scope.
+    private fun createCoroutineScope() = CoroutineScope(Dispatchers.Default + SupervisorJob())
+
     // Processes due jobs and executes them.
     private suspend fun processDueJobs() {
         val now = ZonedDateTime.now(timeZone)

src/test/kotlin/CoroutineExecutorTest.kt

@@ -23,7 +23,6 @@ import dev.starry.ktscheduler.triggers.OneTimeTrigger
 import junit.framework.TestCase.assertTrue
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.UnconfinedTestDispatcher
 import kotlinx.coroutines.test.resetMain
 import kotlinx.coroutines.test.runTest