Added tests for Maybe data type

src/org/rascalmpl/library/lang/rascal/tests/library/util/MaybeTests.rsc

@@ -0,0 +1,62 @@
+module lang::rascal::tests::library::util::MaybeTests
+
+import util::Maybe;
+
+test bool nothingStrEqual(){
+    Maybe[str] x = nothing();
+    Maybe[str] y = nothing();
+    return x == nothing() && y == nothing() && x == y;
+}
+
+test bool just2nothing(){
+    x = just(3);
+    x = nothing();
+    return x == nothing();
+}
+
+test bool inc1(){
+    Maybe[int] x = just(3);
+    x.val += 1;
+    return x.val == 4;
+}
+
+test bool inc2(){
+    x = just(3);
+    x.val += 1;
+    return x.val == 4;
+}
+
+test bool inc3(){
+    x = just((1 : "a"));
+    x.val[1] ? "aaa" += "xxx";
+    return x.val == (1:"axxx");
+}
+
+test bool inc4(){
+    x = just((1 : "a"));
+    x.val[2] ? "aaa" += "xxx";
+    return x.val == (1:"a",2:"aaaxxx");
+}
+
+data X = contain(
+            Maybe[bool] p,
+            Maybe[int] kw1 = just(2),
+            Maybe[str] kw2 = nothing()
+        );
+
+test bool contain1(){
+    c = contain(nothing());
+    return c.p == nothing() && c.kw1.val == 2 && c.kw2 == nothing();
+}
+
+test bool contain2(){
+    c = contain(nothing(), kw1 = nothing(), kw2 = just("hi"));
+    return c.p == nothing() && c.kw1 == nothing() && c.kw2 == just("hi");
+}
+
+test bool contain3(){
+    c = contain(nothing());
+    c.kw1 = nothing();
+    c.kw2 = just("hi");
+    return c.p == nothing() && c.kw1 == nothing() && c.kw2 == just("hi");
+}