Add tests for ViewPureChecker with custom operators

test/libsolidity/syntaxTests/operators/custom/operators_with_pure_modifier.sol

@@ -0,0 +1,26 @@
+type Int is uint8;
+
+using {
+    add as +,
+    sub as -,
+    mul as *
+} for Int;
+
+function f_view() view {}
+
+function add(Int, Int) pure returns (Int) {
+    return Int.wrap(0);
+}
+
+function sub(Int, Int) returns (Int) {
+    return Int.wrap(0);
+}
+
+function mul(Int, Int) pure returns (Int) {
+    f_view();
+    return Int.wrap(0);
+}
+
+// ----
+// Warning 2018: (179-243): Function state mutability can be restricted to pure
+// TypeError 2527: (293-301): Function declared as pure, but this expression (potentially) reads from the environment or state and thus requires "view".

test/libsolidity/syntaxTests/operators/custom/operators_with_view_modifier.sol

@@ -0,0 +1,30 @@
+type Int is uint8;
+
+using {
+    add as +,
+    sub as -,
+    mul as *
+} for Int;
+
+
+function f_view() view {}
+function f() {}
+
+function add(Int, Int) view returns (Int) {
+    f_view();
+    return Int.wrap(0);
+}
+
+function sub(Int, Int) returns (Int) {
+    f_view();
+    return Int.wrap(0);
+}
+
+function mul(Int, Int) view returns (Int) {
+    f();
+    return Int.wrap(0);
+}
+
+// ----
+// Warning 2018: (210-288): Function state mutability can be restricted to view
+// TypeError 8961: (338-341): Function cannot be declared as view because this expression (potentially) modifies the state.