fix(py_test): Support target names with a test_ prefix

examples/pytest/BUILD.bazel

@@ -38,3 +38,13 @@ py_test(
     shard_count = 2,
     deps = ["@pypi_pytest//:pkg"],
 )
+
+py_test(
+    # NB: target name starts with a test_ prefix
+    name = "test_prefix",
+    srcs = ["prefix_test.py"],
+    pytest_main = True,
+    deps = [
+        "@pypi_pytest//:pkg",
+    ],
+)

examples/pytest/prefix_test.py

@@ -0,0 +1,2 @@
+def test_always_passing():
+    assert True

py/defs.bzl

@@ -163,8 +163,11 @@ def py_test(name, srcs = [], main = None, pytest_main = False, **kwargs):
         if main:
             fail("When pytest_main is set, the main attribute should not be set.")
         pytest_main_target = name + ".pytest_main"
-        main = pytest_main_target + ".py"
-        py_pytest_main(name = pytest_main_target)
+
+        # NB: The main name starts with a dot, so pytest does not mistakenly collect
+        # the file during test collection even if the target name starts with `test_`.
+        main = "." + pytest_main_target + ".py"
+        py_pytest_main(name = pytest_main_target, test_main = main)
         srcs.append(main)
         deps.append(pytest_main_target)
 

py/private/py_pytest_main.bzl

@@ -58,19 +58,20 @@ _py_pytest_main = rule(
     },
 )
 
-def py_pytest_main(name, py_library = default_py_library, deps = [], data = [], testonly = True, **kwargs):
+def py_pytest_main(name, test_main = None, py_library = default_py_library, deps = [], data = [], testonly = True, **kwargs):
     """py_pytest_main wraps the template rendering target and the final py_library.
 
     Args:
         name: The name of the runable target that updates the test entry file.
+        test_main: The name of the test entry file to be generated.
         py_library: Use this attribute to override the default py_library rule.
         deps: A list containing the pytest library target, e.g., @pypi_pytest//:pkg.
         data: A list of data dependencies to pass to the py_library target.
         testonly: A boolean indicating if the py_library target is testonly.
         **kwargs: The extra arguments passed to the template rendering target.
     """
 
-    test_main = name + ".py"
+    test_main = test_main or name + ".py"
     tags = kwargs.pop("tags", [])
     visibility = kwargs.pop("visibility", [])