Create simple syntax highlighting tests

compiler/src/dotty/tools/dotc/printing/SyntaxHighlighting.scala

@@ -10,6 +10,7 @@ import util.Chars
 /** This object provides functions for syntax highlighting in the REPL */
 object SyntaxHighlighting {
 
+  // Keep in sync with SyntaxHighlightingTests
   val NoColor         = Console.RESET
   val CommentColor    = Console.BLUE
   val KeywordColor    = Console.YELLOW

compiler/test/dotty/tools/dotc/reporting/SyntaxHighlightingTests.scala

@@ -0,0 +1,62 @@
+package dotty.tools.dotc.printing
+
+import org.junit.Assert._
+import org.junit.Test
+
+/** Adapted from Ammonite HighlightTests
+ */
+class SyntaxHighlightingTests {
+  import SyntaxHighlighting._
+
+  private def test(source: String, expected: String): Unit = {
+    val highlighted = SyntaxHighlighting.apply(source)
+      .mkString
+      .replace(NoColor,         ">")
+      .replace(CommentColor,    "<C|")
+      .replace(KeywordColor,    "<K|")
+      .replace(ValDefColor,     "<V|")
+      .replace(LiteralColor,    "<L|")
+      .replace(StringColor,     "<S|")
+      .replace(TypeColor,       "<T|")
+      // .replace(AnnotationColor, "<A|") // is the same color as type color
+
+    if (expected != highlighted) {
+      // assertEquals produces weird expected/found message
+      fail(s"expected: $expected but was: $highlighted")
+    }
+  }
+
+  @Test
+  def comments = {
+    test("//a", "<C|//a>")
+    test("/** a */", "<C|/** a */>")
+    test("/* a */", "<C|/* a */>")
+  }
+
+  @Test
+  def types = {
+    test("type Foo = Int", "<K|type> <T|Foo> = <T|Int>")
+  }
+
+  @Test
+  def literals = {
+    test("1", "<L|1>")
+    // test("1L", "<L|1L>")
+  }
+
+  @Test
+  def strings = {
+    // For some reason we currently use literal color for string
+    test("\"Hello\"", "<L|\"Hello\">")
+  }
+
+  @Test
+  def annotations = {
+    test("@tailrec", "<T|@tailrec>")
+  }
+
+  @Test
+  def expressions = {
+    test("val x = 1 + 2 + 3", "<K|val> <V|x> = <L|1> + <L|2> + <L|3>")
+  }
+}