Get references compiling, initial tests

tests/assignment.cpp

@@ -1,7 +1,7 @@
 #include "catch.hpp"
 #include "optional.hpp"
 
-TEST_CASE("Assignment", "[assignment]") {
+TEST_CASE("Assignment value", "[assignment.value]") {
     tl::optional<int> o1 = 42;
     tl::optional<int> o2 = 12;
     tl::optional<int> o3;
@@ -32,3 +32,37 @@ TEST_CASE("Assignment", "[assignment]") {
     o1 = std::move(o4);
     REQUIRE(*o1 == 42);
 }
+
+
+TEST_CASE("Assignment reference", "[assignment.ref]") {
+    auto i = 42;
+    auto j = 12;
+    
+    tl::optional<int&> o1 = i;
+    tl::optional<int&> o2 = j;
+    tl::optional<int&> o3;
+
+    o1 = o1;
+    REQUIRE(*o1 == 42);
+    REQUIRE(&*o1 == &i);    
+
+    o1 = o2;
+    REQUIRE(*o1 == 12);
+
+    o1 = o3;
+    REQUIRE(!o1);
+
+    auto k = 42;
+    o1 = k;
+    REQUIRE(*o1 == 42);
+    REQUIRE(*o1 == i);
+    REQUIRE(*o1 == k);        
+    REQUIRE(&*o1 != &i);
+    REQUIRE(&*o1 == &k);            
+
+    o1 = tl::nullopt;
+    REQUIRE(!o1);
+
+    o1 = std::move(o2);
+    REQUIRE(*o1 == 12);
+}