sq: add test, change error msg

tests/discover/libraries/data/certificate.fmf

@@ -63,6 +63,14 @@ test: ./certificate.sh
         require:
           - url: https://github.com/psss/try
             type: library
+    /node-metadata:
+        summary: Path exists but node of such name not
+        require:
+          - url: https://github.com/teemtee/tests
+            type: library
+            ref: missing-node-data
+            name: /dir-without-fmf
+            path: /nested
     /reference:
         summary: Requested reference does not exist
         require:

tests/discover/libraries/data/plan.fmf

@@ -64,6 +64,11 @@ execute:
             summary: "Missing reference"
             discover+:
                 test: missing/reference
+        /node-metadata:
+            summary: "Missing node with such name, but path exists"
+            discover+:
+                test: missing/node-metadata
+
 
 /querying:
     summary: "Many tests requiring same rpm-only library"

tmt/libraries/beakerlib.py

@@ -332,8 +332,8 @@ def fetch(self) -> None:
                             f'url: {self.url}' if self.url else None,
                             f'ref: {self.ref}' if self.ref else None,
                             f'path: {self.path}' if self.path else None] if s is not None])
-                        raise tmt.utils.SpecificationError(f"Can't find library @ {fmf_id}.") \
-                            from error
+                        raise tmt.utils.SpecificationError(
+                            f"Library with {fmf_id=} doesn't exist.") from error
 
                     # Copy fmf metadata
                     shutil.copytree(clone_dir / '.fmf', directory / '.fmf', dirs_exist_ok=True)