Add test for expected<void> relational operators (#51, thanks @Crzyrndm)

README.md

@@ -450,6 +450,7 @@ expected<void>: Allows to observe its error as unexpected
 expected<void>: Allows to query if it contains an exception of a specific base type
 expected<void>: Throws bad_expected_access on value access when disengaged
 operators: Provides expected relational operators
+operators: Provides expected relational operators (void)
 swap: Allows expected to be swapped
 std::hash: Allows to compute hash value for expected
 tweak header: reads tweak header if supported [tweak]

test/expected.t.cpp

@@ -647,6 +647,7 @@ CASE( "expected: Allows to move-construct from expected: value" )
 
     EXPECT( b              );
     EXPECT( b.value() == 7 );
+    EXPECT( a              );   // postcondition: unchanged!
 }
 
 CASE( "expected: Allows to move-construct from expected: error" )
@@ -1247,6 +1248,7 @@ CASE( "expected<void>: Allows to move-construct from expected<void>: value" )
     expected<void, int> b{ std::move( a ) };
 
     EXPECT( b );
+    EXPECT( a );    // postcondition: unchanged!
 }
 
 CASE( "expected<void>: Allows to move-construct from expected<void>: error" )
@@ -1589,6 +1591,25 @@ CASE( "operators: Provides expected relational operators" )
     }
 }
 
+CASE( "operators: Provides expected relational operators (void)" )
+{
+    SETUP( "" ) {
+        expected<void, char> ev1;
+        expected<void, char> ev2;
+        expected<void, char> evu{ unexpect };
+
+    // compare engaged expected with engaged expected
+
+    SECTION( "  engaged == engaged"     ) { EXPECT(     ev1 == ev2 ); }
+    SECTION( "!(engaged != engaged)"    ) { EXPECT_NOT( ev1 != ev2 ); }
+
+    // compare engaged expected with disengaged expected
+
+    SECTION( "  engaged != disengaged"  ) { EXPECT(     ev1 != evu ); }
+    SECTION( "!(engaged == disengaged)" ) { EXPECT_NOT( ev1 == evu ); }
+    }
+}
+
 // -----------------------------------------------------------------------
 // expected: specialized algorithms