[llvm] Unittest for Error forwarding, follow-up to PR #92208 (PR #92314)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: Mircea Trofin (mtrofin)

<details>
<summary>Changes</summary>

Added a unittest demonstrating Error -> Expected<T> forwarding.

---
Full diff: https://github.com/llvm/llvm-project/pull/92314.diff


1 Files Affected:

- (modified) llvm/unittests/Support/ErrorTest.cpp (+16) 


``````````diff
diff --git a/llvm/unittests/Support/ErrorTest.cpp b/llvm/unittests/Support/ErrorTest.cpp
index 1229282cf0def..5c0179f256d6e 100644
--- a/llvm/unittests/Support/ErrorTest.cpp
+++ b/llvm/unittests/Support/ErrorTest.cpp
@@ -1158,4 +1158,20 @@ TEST(Error, BadAllocFatalErrorHandlersInteraction) {
   remove_bad_alloc_error_handler();
 }
 
+TEST(Error, ForwardToExpected) {
+  auto ErrorReturningFct = [](bool Fail) {
+    return Fail ? make_error<StringError>(llvm::errc::invalid_argument,
+                                          "Some Error")
+                : Error::success();
+  };
+  auto ExpectedReturningFct = [&](bool Fail) -> Expected<int> {
+    auto Err = ErrorReturningFct(Fail);
+    if (Err)
+      return Err;
+    return 42;
+  };
+  std::optional<int> MaybeV;
+  EXPECT_THAT_ERROR(ExpectedReturningFct(true).moveInto(MaybeV), Failed());
+  EXPECT_EQ(*ExpectedReturningFct(false), 42);
+}
 } // namespace

``````````

</details>


https://github.com/llvm/llvm-project/pull/92314