[kotlin-test] Enable explicit API mode KT-61969

libraries/kotlin.test/build.gradle.kts

@@ -36,6 +36,8 @@ val jvmTestFrameworks = JvmTestFramework.values().toList()
 
 kotlin {
 
+    explicitApi()
+
     jvm {
         compilations {
             all {
@@ -58,6 +60,11 @@ kotlin {
             jvmTestFrameworks.forEach { framework ->
                 val frameworkMain = create("$framework") {
                     associateWith(main)
+                    compileTaskProvider.configure {
+                        compilerOptions {
+                            freeCompilerArgs.add("-Xexplicit-api=strict")
+                        }
+                    }
                 }
                 create("${framework}Test") {
                     associateWith(frameworkMain)

libraries/kotlin.test/junit/src/main/kotlin/JUnitSupport.kt

@@ -11,7 +11,7 @@ import kotlin.test.*
 /**
  * Provides [JUnitAsserter] if `org.junit.Assert` is found in the classpath.
  */
-class JUnitContributor : AsserterContributor {
+public class JUnitContributor : AsserterContributor {
     override fun contribute(): Asserter? {
         return if (hasJUnitInClassPath) JUnitAsserter else null
     }
@@ -27,7 +27,7 @@ class JUnitContributor : AsserterContributor {
 /**
  * Implements `kotlin.test` assertions by delegating them to `org.junit.Assert` class.
  */
-object JUnitAsserter : Asserter {
+public object JUnitAsserter : Asserter {
     override fun assertEquals(message: String?, expected: Any?, actual: Any?) {
         Assert.assertEquals(message, expected, actual)
     }

libraries/kotlin.test/junit5/src/main/kotlin/JUnitSupport.kt

@@ -11,7 +11,7 @@ import kotlin.test.*
 /**
  * Provides [JUnit5Asserter] if `org.junit.jupiter.api.Assertions` class is found in the classpath.
  */
-class JUnit5Contributor : AsserterContributor {
+public class JUnit5Contributor : AsserterContributor {
     override fun contribute(): Asserter? {
         return if (hasJUnitInClassPath) JUnit5Asserter else null
     }
@@ -27,7 +27,7 @@ class JUnit5Contributor : AsserterContributor {
 /**
  * Implements `kotlin.test` assertions by delegating them to `org.junit.jupiter.api.Assertions` class.
  */
-object JUnit5Asserter : Asserter {
+public object JUnit5Asserter : Asserter {
     override fun assertEquals(message: String?, expected: Any?, actual: Any?) {
         Assertions.assertEquals(expected, actual, message)
     }

libraries/kotlin.test/testng/src/main/kotlin/TestNGSupport.kt

@@ -11,7 +11,7 @@ import kotlin.test.*
 /**
  * Provides [TestNGAsserter] if `org.testng.Assert` is found in the classpath.
  */
-class TestNGContributor : AsserterContributor {
+public class TestNGContributor : AsserterContributor {
     override fun contribute(): Asserter? {
         return if (hasTestNGInClassPath) TestNGAsserter else null
     }
@@ -27,7 +27,7 @@ class TestNGContributor : AsserterContributor {
 /**
  * Implements `kotlin.test` assertions by delegating them to `org.testng.Assert` class.
  */
-object TestNGAsserter : Asserter {
+public object TestNGAsserter : Asserter {
     override fun assertEquals(message: String?, expected: Any?, actual: Any?) {
         Assert.assertEquals(actual, expected, message)
     }