Fix #3071: add test for missing output directory

Author: esarbe

compiler/test/dotty/tools/dotc/SettingsTests.scala

@@ -0,0 +1,14 @@
+package dotty.tools.dotc
+
+import org.junit.Test
+import org.junit.Assert._
+
+class SettingsTests {
+
+  @Test def missingOutputDir: Unit = {
+    val options = Array("-d", "not_here")
+    val reporter = Main.process(options)
+    assertEquals(1, reporter.errorCount)
+    assertEquals("'not_here' does not exist or is not a directory", reporter.allErrors.head.message)
+  }
+}