[Test] Add a simple test case for a method with an opaque return type

and no return statements.

Author: hborla

test/type/opaque.swift

@@ -172,8 +172,10 @@ func recursion(x: Int) -> some P {
   return recursion(x: x - 1)
 }
 
-func noReturnStmts() -> some P { // expected-note {{opaque return type declared here}}
-    fatalError() // expected-error{{return type of global function 'noReturnStmts()' requires that 'Never' conform to 'P'}}
+func noReturnStmts() -> some P {} // expected-error {{function declares an opaque return type, but has no return statements in its body from which to infer an underlying type}}
+
+func returnUninhabited() -> some P { // expected-note {{opaque return type declared here}}
+    fatalError() // expected-error{{return type of global function 'returnUninhabited()' requires that 'Never' conform to 'P'}}
 }
 
 func mismatchedReturnTypes(_ x: Bool, _ y: Int, _ z: String) -> some P { // expected-error{{do not have matching underlying types}}