[llvm] [llvm/CAS] Improve layering and decouple `UnifiedOnDiskCache` from the builtin hash implementation (PR #177280)

[Nico Weber via llvm-commits]

================
@@ -42,25 +42,29 @@ static Expected<size_t> countFileSizes(StringRef Path) {
   return TotalSize;
 }
 
-TEST_F(OnDiskCASTest, UnifiedOnDiskCacheTest) {
+TEST_P(CustomHasherOnDiskCASTest, UnifiedOnDiskCacheTest) {
----------------
nico wrote:

I'm getting a bunch of

```
../../llvm/unittests/CAS/UnifiedOnDiskCacheTest.cpp:45: Failure
Parameterized test suite CustomHasherOnDiskCASTest is defined via TEST_P, but never instantiated. None of the test cases will run. Either no INSTANTIATE_TEST_SUITE_P is provided or the only ones provided expand to nothing.

Ideally, TEST_P definitions should only ever be included as part of binaries that intend to use them. (As opposed to, for example, being placed in a library that may be linked in to get other utilities.)

To suppress this error for this test suite, insert the following line (in a non-header) in the namespace it is defined in:

GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(CustomHasherOnDiskCASTest);
```

and looking at the diff, that seems accurate. Did you try running this test locally?

https://github.com/llvm/llvm-project/pull/177280