[llvm] [NFC][ADT] Introduce a test harness for StringRefTest (PR #105500)

[Sergei Barannikov via llvm-commits]

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@@ -47,37 +34,39 @@ static_assert(std::is_assignable_v<StringRef &, const char *&&>,
 static_assert(std::is_assignable_v<StringRef &, const char *&>,
               "Assigning from lvalue C string");
 
-namespace {
-TEST(StringRefTest, Construction) {
+// Test fixture.
+class StringRefTest : public testing::Test {};
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s-barannikov wrote:

Why do you need it with no methods?

https://github.com/llvm/llvm-project/pull/105500