Add assume function to abort tests instead of failing them

jvm only, uses open4j's TestAbortedException under the hood so works on
junit5 or other compatible testing framework (does not work on junit4)

Fixes #432

assertk/build.gradle.kts

@@ -64,3 +64,7 @@ kotlin {
         }
     }
 }
+
+tasks.withType<Test>().configureEach {
+    useJUnitPlatform()
+}

assertk/src/jvmMain/kotlin/assertk/assume.kt

@@ -0,0 +1,15 @@
+package assertk
+
+/**
+ * Aborts the test instead of failing it, this gives you a way to skip tests based on a dynamic assertion.
+ *
+ * ```
+ * // only run test on windows
+ * assume {
+ *     assertThat(System.getProperty("os.name")).startsWith("Windows")
+ * }
+ * ```
+ */
+fun assume(f: () -> Unit) {
+    AssumptionFailure.run { f() }
+}

assertk/src/jvmMain/kotlin/assertk/failure.kt

@@ -3,6 +3,9 @@
 
 package assertk
 
+import com.willowtreeapps.opentest4k.AssertionFailedError
+import com.willowtreeapps.opentest4k.TestAbortedException
+
 internal actual inline fun failWithNotInStacktrace(error: Throwable): Nothing {
     val filtered = error.stackTrace
         .dropWhile { it.className.startsWith("assertk") }
@@ -16,3 +19,21 @@ internal actual inline fun failWithNotInStacktrace(error: Throwable): Nothing {
 internal actual inline fun Throwable.isFatal(): Boolean =
     // https://github.com/ReactiveX/RxJava/blob/6a44e5d0543a48f1c378dc833a155f3f71333bc2/src/main/java/io/reactivex/exceptions/Exceptions.java#L66
     this is VirtualMachineError || this is ThreadDeath || this is LinkageError
+
+internal object AssumptionFailure : Failure {
+    override fun fail(error: Throwable) {
+        failWithNotInStacktrace(
+            TestAbortedException(
+                buildString {
+                    append("Assumption failed")
+                    error.message?.let { message ->
+                        append(": ")
+                        append(message)
+                    }
+                },
+                // unwrap assertion errors
+                if (error is AssertionFailedError) error.cause else error
+            )
+        )
+    }
+}

assertk/src/jvmTest/kotlin/test/assertk/JVMAssertAllTest.kt

@@ -4,9 +4,9 @@ import assertk.all
 import assertk.assertAll
 import assertk.assertThat
 import assertk.assertions.*
-import org.junit.Test
 import java.util.concurrent.Executors
 import java.util.concurrent.TimeUnit
+import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 import kotlin.test.assertFalse

assertk/src/jvmTest/kotlin/test/assertk/assertions/AssumeTest.kt

@@ -0,0 +1,28 @@
+package test.assertk.assertions
+
+import assertk.assertThat
+import assertk.assertions.isFalse
+import assertk.assume
+import com.willowtreeapps.opentest4k.TestAbortedException
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+class AssumeTest {
+    @Test
+    fun assume_throws_TestAbortedException() {
+        val error = assertFailsWith<TestAbortedException> {
+            assume {
+                assertThat(true).isFalse()
+            }
+        }
+
+        assertEquals("Assumption failed: expected to be false", error.message)
+    }
+
+    @Test
+    fun assume_aborts_instead_of_fails_test() {
+        // this test should be skipped instead of failing
+        assume { assertThat(true).isFalse() }
+    }
+}

assertk/src/jvmTest/kotlin/test/assertk/assertions/JVMResultTest.kt

@@ -2,8 +2,8 @@ package test.assertk.assertions
 
 import assertk.assertThat
 import assertk.assertions.isSuccess
-import org.junit.Test
 import test.assertk.exceptionPackageName
+import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 import kotlin.test.assertNotNull

assertk/src/jvmTest/kotlin/test/assertk/assertions/OptionalTest.kt

@@ -4,10 +4,10 @@ import assertk.all
 import assertk.assertAll
 import assertk.assertThat
 import assertk.assertions.*
-import org.junit.Test
 import java.time.LocalDate
 import java.time.Month
 import java.util.*
+import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith
 

assertk/src/jvmTest/kotlin/test/assertk/assertions/support/JavaNumberTest.kt

@@ -4,9 +4,9 @@ import assertk.assertThat
 import assertk.assertions.isNegative
 import assertk.assertions.isPositive
 import assertk.assertions.isZero
-import org.junit.Test
 import java.math.BigDecimal
 import java.math.BigInteger
+import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFailsWith