Resolve "Refactor debug messages from System.out to SLF4J"

Closes #46 (closed)

ragconnect.tests/src/test/java/org/jastadd/ragconnect/tests/Errors.java

@@ -53,10 +53,10 @@ public class Errors {
         .collect(Collectors.toList());
     Path outPath = TestUtils.runCompiler(grammarFile, connectFiles, rootNode, ERROR_DIRECTORY, 1);
 
-    final String startOfErrorsPattern = "SEVERE: Errors:";
+    final String startOfErrorsPattern = "Errors:\n";
     String out = readFile(outPath, Charset.defaultCharset());
     assertThat(out).contains(startOfErrorsPattern);
-    out = out.substring(out.indexOf(startOfErrorsPattern) + 16);
+    out = out.substring(out.indexOf(startOfErrorsPattern) + startOfErrorsPattern.length());
 
     Path expectedPath = Paths.get(TestUtils.INPUT_DIRECTORY_PREFIX)
         .resolve(ERROR_DIRECTORY)