Re: [PATCH 01/11] t: add helpers to test for reference existence

> There are two major ways to check for the existence of a reference in
> our tests:
>
>     - `git rev-parse --verify` can be used to check for existence of a
>       reference. This only works in the case where the reference is well
>       formed though and resolves to an actual object ID. This does not
>       work with malformed reference names or invalid contents.
>
>     - `test_path_is_file` can be used to check for existence of a loose
>       reference if it is known to not resolve to an actual object ID. It
>       by necessity reaches into implementation details of the reference
>       backend though.

> Similarly, there are two equivalent ways to check for the absence of a
> reference:
>
>     - `test_must_fail git rev-parse` can be used to check for the
>       absence of a reference. It could fail due to a number of reasons
>       though, and all of these reasons will be thrown into the same bag
>       as an absent reference.
>
>     - `test_path_is_missing` can be used to check explicitly for the
>       absence of a loose reference, but again reaches into internal
>       implementation details of the reference backend.
>
> So both our tooling to check for the presence and for the absence of
> references in tests is lacking as either failure cases are thrown into
> the same bag or we need to reach into internal implementation details of
> the respective reference backend.

> Introduce a new subcommand for our ref-store test helper that explicitly
> checks only for the presence or absence of a reference. This addresses
> these limitations:
>
>     - We can check for the presence of references with malformed names.

> diff --git a/t/README b/t/README
> index 61080859899..779f7e7dd86 100644
> --- a/t/README
> +++ b/t/README
> @@ -928,6 +928,15 @@ see test-lib-functions.sh for the full list and their options.
>     committer times to defined state.  Subsequent calls will
>     advance the times by a fixed amount.
>  
> + - test_ref_exists <ref>, test_ref_missing <ref>
> +
> +   Check whether a reference exists or is missing. In contrast to
> +   git-rev-parse(1), these helpers also work with invalid reference
> +   names and references whose contents are unresolvable. The latter
> +   function also distinguishes generic errors from the case where a
> +   reference explicitly doesn't exist and is thus safer to use than
> +   `test_must_fail git rev-parse`.
> +
>   - test_commit <message> [<filename> [<contents>]]
>  
>     Creates a commit with the given message, committing the given
> diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c
> index 48552e6a9e0..7400f560ab6 100644
> --- a/t/helper/test-ref-store.c
> +++ b/t/helper/test-ref-store.c
> @@ -1,6 +1,6 @@
>  #include "test-tool.h"
>  #include "hex.h"
> -#include "refs.h"
> +#include "refs/refs-internal.h"
>  #include "setup.h"
>  #include "worktree.h"
>  #include "object-store-ll.h"
> @@ -221,6 +221,30 @@ static int cmd_verify_ref(struct ref_store *refs, const char **argv)
>  	return ret;
>  }
>  
> +static int cmd_ref_exists(struct ref_store *refs, const char **argv)
> +{
> +	const char *refname = notnull(*argv++, "refname");
> +	struct strbuf unused_referent = STRBUF_INIT;
> +	struct object_id unused_oid;
> +	unsigned int unused_type;
> +	int failure_errno;
> +
> +	if (refs_read_raw_ref(refs, refname, &unused_oid, &unused_referent,
> +			      &unused_type, &failure_errno)) {
> +		/*
> +		 * We handle ENOENT separately here such that it is possible to
> +		 * distinguish actually-missing references from any kind of
> +		 * generic error.
> +		 */
> +		if (failure_errno == ENOENT)
> +			return 17;