Move to JUnit 5.2.0 (#99)

* Bump to JUnit 5.2, Gradle 4.8 & AGP 3.2.0-alpha17 to ensure compatibility
* Bump minimum Gradle requirement to 4.7
* Bump a whole lot of other dependencies & move to AS 3.2
* Port FunctionalSpec to Kotlin
* Remove dependency on Spock
* Introduce semver check library & apply new nullability settings

Author: Marcel Schnelle

.idea/codeStyleSettings.xml

@@ -1,6 +1,5 @@
 import de.mannodermaus.gradle.plugins.junit5.WriteClasspathResource
 import org.apache.tools.ant.filters.ReplaceTokens
-import org.junit.platform.console.options.Details
 
 apply plugin: "groovy"
 apply plugin: "java-gradle-plugin"
@@ -55,10 +54,13 @@ test {
 }
 
 junitPlatform {
-  details Details.TREE
+  details "tree"
   enableStandardTestTask true
 }
 
+// Enable this line to run slow Functional Tests on the local device as well
+//junitPlatformTest.environment("CI", "true")
+
 dependencies {
   // Test Plugin Dependencies
   testImplementation project(":android-junit5")
@@ -74,17 +76,15 @@ dependencies {
   // Test Execution
   testImplementation "junit:junit:$JUNIT4_VERSION"
   testImplementation "org.junit.jupiter:junit-jupiter-api:$JUNIT_JUPITER_VERSION"
+  testImplementation "org.junit.jupiter:junit-jupiter-params:$JUNIT_JUPITER_VERSION"
   testRuntimeOnly "org.junit.jupiter:junit-jupiter-engine:$JUNIT_JUPITER_VERSION"
   testImplementation "org.jetbrains.spek:spek-api:$SPEK_VERSION"
   testRuntimeOnly "org.jetbrains.spek:spek-junit-platform-engine:$SPEK_VERSION"
+  testImplementation "org.junit-pioneer:junit-pioneer:$JUNIT_PIONEER_VERSION"
 
   testImplementation "org.assertj:assertj-core:$ASSERTJ_VERSION"
   testImplementation "org.mockito:mockito-core:$MOCKITO_VERSION"
 
-  testImplementation("org.spockframework:spock-core:$SPOCK_VERSION") {
-    exclude group: "org.codehaus.groovy"
-  }
-
   // Compilation of local classpath for functional tests
   functionalTest "junit:junit:$JUNIT4_VERSION"
   functionalTest "com.android.tools.build:gradle:$ANDROID_PLUGIN_VERSION"