Add uncovered test and replace uncovered tests by asserts

test/libsolidity/smtCheckerTests/operators/bitwise_not_fixed_bytes.sol

@@ -1,7 +1,12 @@
 pragma experimental SMTChecker;
+
 contract C {
-  function f() public pure returns (byte) {
-    return (~byte(0xFF));
-  }
+	function f() public pure {
+		// ffff0000 in bytes4
+		bytes4 x = ~bytes4(hex"ffff");
+		assert(x == 0xffff0000); // should fail
+		assert(x == 0x0000ffff); // should hold
+	}
 }
 // ----
+// Warning 6328: (175-198): CHC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/operators/exp.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+contract D {
+	function f(uint x) public pure {
+		assert(x**2 == 4);
+	}
+}
+// ----
+// Warning 5188: (88-92): Assertion checker does not yet implement this operator.
+// Warning 6328: (81-98): CHC: Assertion violation happens here.
+// Warning 5188: (88-92): Assertion checker does not yet implement this operator.