show bytes as hex on all supported platforms (#498)

assertk/src/nativeMain/kotlin/assertk/assertions/support/support.kt

@@ -1,5 +1,15 @@
 package assertk.assertions.support
 
 internal actual fun displayPlatformSpecific(value: Any?): String {
-    return value.toString()
+    return when (value) {
+        is Byte -> formatHex(value)
+        else -> value.toString()
+    }
 }
+
+//TODO: replace with HexFormat when stable
+private fun formatHex(byte: Byte) : String {
+    val topNibble = (byte.toInt() and 0xF0) ushr 4
+    val bottomNibble = byte.toInt() and 0x0F
+    return "0x${topNibble.toString(16).uppercase()}${bottomNibble.toString(16).uppercase()}"
+}

assertk/src/nativeTest/kotlin/test/assertk/assertions/support/NativeSupportTest.kt

@@ -0,0 +1,13 @@
+package test.assertk.assertions.support
+
+import assertk.assertions.support.show
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class NativeSupportTest {
+
+    @Test fun show_byte_array() {
+        assertEquals("<[0x0A, 0x0F]>", show(byteArrayOf(10, 15)))
+    }
+
+}

assertk/src/wasmJsMain/kotlin/assertk/assertions/support/support.kt

@@ -1,5 +1,15 @@
 package assertk.assertions.support
 
 internal actual fun displayPlatformSpecific(value: Any?): String {
-    return value.toString()
+    return when (value) {
+        is Byte -> formatHex(value)
+        else -> value.toString()
+    }
 }
+
+//TODO: replace with HexFormat when stable
+private fun formatHex(byte: Byte) : String {
+    val topNibble = (byte.toInt() and 0xF0) ushr 4
+    val bottomNibble = byte.toInt() and 0x0F
+    return "0x${topNibble.toString(16).uppercase()}${bottomNibble.toString(16).uppercase()}"
+}

assertk/src/wasmJsTest/kotlin/test/assertk/assertions/support/WasmJsSupportTest.kt

@@ -0,0 +1,12 @@
+package test.assertk.assertions.support
+
+import assertk.assertions.support.show
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class WasmJsSupportTest {
+
+    @Test fun show_byte_array() {
+        assertEquals("<[0x0A, 0x0F]>", show(byteArrayOf(10, 15)))
+    }
+}