Add a unit test for the regular expression engine

We still do not parse the regular expression patterns, but we can at
least test that the hardcoded 'a(bb)+a' works as expected.

This class will be extended as we support more and more features.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

test/Regex.java

@@ -0,0 +1,26 @@
+import regex.Matcher;
+import regex.Pattern;
+
+public class Regex {
+  private static void expect(boolean v) {
+    if (! v) throw new RuntimeException();
+  }
+
+  private static Matcher getMatcher(String regex, String string) {
+    return Pattern.compile(regex).matcher(string);
+  }
+
+  private static void expectMatch(String regex, String string) {
+    expect(getMatcher(regex, string).matches());
+  }
+
+  private static void expectNoMatch(String regex, String string) {
+    expect(!getMatcher(regex, string).matches());
+  }
+
+  public static void main(String[] args) {
+    expectMatch("a(bb)?a", "abba");
+    expectNoMatch("a(bb)?a", "abbba");
+    expectNoMatch("a(bb)?a", "abbaa");
+  }
+}