Tweak test per review; prefer assert to print

[Cherry-picked f73185f]

Author: som-snytt

tests/run/i23693.check

@@ -1,17 +1,22 @@
 //> using options -Wtostring-interpolated
 
-// verify warning messages and runtime result
+// verify ~warning messages and~ runtime result
 // never mind, the test rig doesn't log diagnostics! unlike beloved partest.
 
+// Sadly, junit is not available.
+//import org.junit.Assert.assertEquals as jassert
+
+def assertEquals(expected: String)(actual: String): Unit = assert(expected == actual)
+
 case class K(i: Int)
 
 @main def Test =
   val k = K(42)
-  println:
+  assertEquals("k == K(42)"):
     s"k == $k"
-  println:
+  assertEquals("\\k == \\K(42)"):
     raw"\k == \$k"
-  println:
+  assertEquals("k == K(42)"):
     f"k == $k"
-  println:
+  assertEquals("k == K(42)"):
     f"k == $k%s"

tests/run/i23693.scala

@@ -1,6 +1,6 @@
 //> using options -Wtostring-interpolated
 
-// verify warning messages and runtime result
+// verify warning messages; cf run test; we must verify runtime while warning.
 
 case class K(i: Int):
   def show: Unit = ()