Demonstrate how to use BUILD files as test inputs

Author: benjyw

BUILD

@@ -5,3 +5,8 @@
 # `python_requirement_library` target. Refer to
 # https://www.pantsbuild.org/docs/python-third-party-dependencies.
 python_requirements(name="reqs")
+
+files(name="library_build_files", sources=["helloworld/**/BUILD"])
+
+python_tests(name="tests", dependencies=[":library_build_files"])
+

library_build_files_test.py

@@ -0,0 +1,16 @@
+
+import importlib.resources
+
+def test_library_build_files() -> None:
+    def iterate(traversable: importlib.resources.abc.Traversable):
+        for item in traversable.iterdir():
+            if item.is_dir():
+                iterate(item)
+            elif item.name == "BUILD":
+                print(f"Validating {item}")
+                with item.open("r") as fp:
+                    content = fp.read()
+                    print(f"  Content: {content}")
+                    print("-------------------------")
+
+    iterate(importlib.resources.files("helloworld"))

pants.toml

@@ -4,7 +4,7 @@
 [GLOBAL]
 pants_version = "2.26.0"
 backend_packages.add = [
-  "pants.backend.build_files.fmt.black",  
+  "pants.backend.build_files.fmt.black",
   "pants.backend.python",
   "pants.backend.python.lint.docformatter",
   "pants.backend.python.lint.black",
@@ -29,7 +29,7 @@ root_patterns = ["/"]
 # Modify this if you don't have Python 3.9 on your machine.
 # This can be a range, such as [">=3.8,<3.11"], but it's usually recommended to restrict
 # to a single minor version.
-interpreter_constraints = ["==3.9.*"]
+interpreter_constraints = ["==3.11.*"]
 
 # Enable the "resolves" mechanism, which turns on lockfiles for user code. See
 # https://www.pantsbuild.org/docs/python-third-party-dependencies. This also adds the