Add tests to ensure that issue #2420 is resolved

The issue was probably fixed by ff32d5f7. Closes #2420.

tests/ui/eq_op.rs

@@ -89,6 +89,12 @@ fn main() {
     let z = x & &y;
 
     check_ignore_macro();
+
+    // named constants
+    const A: u32 = 10;
+    const B: u32 = 10;
+    const C: u32 = A / B; // ok, different named constants
+    const D: u32 = A / A;
 }
 
 macro_rules! check_if_named_foo {

tests/ui/eq_op.stderr

@@ -204,5 +204,11 @@ error: taken reference of right operand
    |
    = note: `-D op-ref` implied by `-D warnings`
 
-error: aborting due to 33 previous errors
+error: equal expressions as operands to `/`
+  --> $DIR/eq_op.rs:97:20
+   |
+97 |     const D: u32 = A / A;
+   |                    ^^^^^
+
+error: aborting due to 34 previous errors