diff --git a/mypy/build.py b/mypy/build.py
index bd9fc43914db..6b0e4a9faa86 100644
--- a/mypy/build.py
+++ b/mypy/build.py
@@ -705,8 +705,8 @@ def __init__(
         self.quickstart_state = read_quickstart_file(options, self.stdout)
         # Fine grained targets (module top levels and top level functions) processed by
         # the semantic analyzer, used only for testing. Currently used only by the new
-        # semantic analyzer.
-        self.processed_targets: list[str] = []
+        # semantic analyzer. Tuple of module and target name.
+        self.processed_targets: list[tuple[str, str]] = []
         # Missing stub packages encountered.
         self.missing_stub_packages: set[str] = set()
         # Cache for mypy ASTs that have completed semantic analysis
diff --git a/mypy/semanal_main.py b/mypy/semanal_main.py
index a5e85878e931..912851520958 100644
--- a/mypy/semanal_main.py
+++ b/mypy/semanal_main.py
@@ -218,7 +218,7 @@ def process_top_levels(graph: Graph, scc: list[str], patches: Patches) -> None:
             state = graph[next_id]
             assert state.tree is not None
             deferred, incomplete, progress = semantic_analyze_target(
-                next_id, state, state.tree, None, final_iteration, patches
+                next_id, next_id, state, state.tree, None, final_iteration, patches
             )
             all_deferred += deferred
             any_progress = any_progress or progress
@@ -289,7 +289,7 @@ def process_top_level_function(
             # OK, this is one last pass, now missing names will be reported.
             analyzer.incomplete_namespaces.discard(module)
         deferred, incomplete, progress = semantic_analyze_target(
-            target, state, node, active_type, final_iteration, patches
+            target, module, state, node, active_type, final_iteration, patches
         )
         if final_iteration:
             assert not deferred, "Must not defer during final iteration"
@@ -318,6 +318,7 @@ def get_all_leaf_targets(file: MypyFile) -> list[TargetInfo]:
 
 def semantic_analyze_target(
     target: str,
+    module: str,
     state: State,
     node: MypyFile | FuncDef | OverloadedFuncDef | Decorator,
     active_type: TypeInfo | None,
@@ -331,7 +332,7 @@ def semantic_analyze_target(
     - was some definition incomplete (need to run another pass)
     - were any new names defined (or placeholders replaced)
     """
-    state.manager.processed_targets.append(target)
+    state.manager.processed_targets.append((module, target))
     tree = state.tree
     assert tree is not None
     analyzer = state.manager.semantic_analyzer
diff --git a/mypy/test/data.py b/mypy/test/data.py
index 6e2ad198f614..3ee368869095 100644
--- a/mypy/test/data.py
+++ b/mypy/test/data.py
@@ -41,6 +41,14 @@ class DeleteFile(NamedTuple):
 FileOperation: _TypeAlias = Union[UpdateFile, DeleteFile]
 
 
+def _file_arg_to_module(filename: str) -> str:
+    filename, _ = os.path.splitext(filename)
+    parts = filename.split("/")  # not os.sep since it comes from test data
+    if parts[-1] == "__init__":
+        parts.pop()
+    return ".".join(parts)
+
+
 def parse_test_case(case: DataDrivenTestCase) -> None:
     """Parse and prepare a single case from suite with test case descriptions.
 
@@ -65,22 +73,26 @@ def parse_test_case(case: DataDrivenTestCase) -> None:
     rechecked_modules: dict[int, set[str]] = {}  # from run number module names
     triggered: list[str] = []  # Active triggers (one line per incremental step)
     targets: dict[int, list[str]] = {}  # Fine-grained targets (per fine-grained update)
+    test_modules: list[str] = []  # Modules which are deemed "test" (vs "fixture")
 
     # Process the parsed items. Each item has a header of form [id args],
     # optionally followed by lines of text.
     item = first_item = test_items[0]
+    test_modules.append("__main__")
     for item in test_items[1:]:
-        if item.id in {"file", "outfile", "outfile-re"}:
+        if item.id in {"file", "fixture", "outfile", "outfile-re"}:
             # Record an extra file needed for the test case.
             assert item.arg is not None
             contents = expand_variables("\n".join(item.data))
-            file_entry = (join(base_path, item.arg), contents)
-            if item.id == "file":
-                files.append(file_entry)
+            path = join(base_path, item.arg)
+            if item.id != "fixture":
+                test_modules.append(_file_arg_to_module(item.arg))
+            if item.id in {"file", "fixture"}:
+                files.append((path, contents))
             elif item.id == "outfile-re":
-                output_files.append((file_entry[0], re.compile(file_entry[1].rstrip(), re.S)))
-            else:
-                output_files.append(file_entry)
+                output_files.append((path, re.compile(contents.rstrip(), re.S)))
+            elif item.id == "outfile":
+                output_files.append((path, contents))
         elif item.id == "builtins":
             # Use an alternative stub file for the builtins module.
             assert item.arg is not None
@@ -207,6 +219,7 @@ def parse_test_case(case: DataDrivenTestCase) -> None:
     case.triggered = triggered or []
     case.normalize_output = normalize_output
     case.expected_fine_grained_targets = targets
+    case.test_modules = test_modules
 
 
 class DataDrivenTestCase(pytest.Item):
@@ -225,6 +238,8 @@ class DataDrivenTestCase(pytest.Item):
 
     # (file path, file content) tuples
     files: list[tuple[str, str]]
+    # Modules which is to be considered "test" rather than "fixture"
+    test_modules: list[str]
     expected_stale_modules: dict[int, set[str]]
     expected_rechecked_modules: dict[int, set[str]]
     expected_fine_grained_targets: dict[int, list[str]]
diff --git a/mypy/test/testcheck.py b/mypy/test/testcheck.py
index 4fe2ee6393c0..5f128283a190 100644
--- a/mypy/test/testcheck.py
+++ b/mypy/test/testcheck.py
@@ -11,7 +11,6 @@
 from mypy.errors import CompileError
 from mypy.modulefinder import BuildSource, FindModuleCache, SearchPaths
 from mypy.options import TYPE_VAR_TUPLE, UNPACK
-from mypy.semanal_main import core_modules
 from mypy.test.config import test_data_prefix, test_temp_dir
 from mypy.test.data import DataDrivenTestCase, DataSuite, FileOperation, module_from_path
 from mypy.test.helpers import (
@@ -188,12 +187,10 @@ def run_case_once(
             if incremental_step:
                 name += str(incremental_step + 1)
             expected = testcase.expected_fine_grained_targets.get(incremental_step + 1)
-            actual = res.manager.processed_targets
-            # Skip the initial builtin cycle.
             actual = [
-                t
-                for t in actual
-                if not any(t.startswith(mod) for mod in core_modules + ["mypy_extensions"])
+                target
+                for module, target in res.manager.processed_targets
+                if module in testcase.test_modules
             ]
             if expected is not None:
                 assert_target_equivalence(name, expected, actual)
diff --git a/mypy/test/testdeps.py b/mypy/test/testdeps.py
index 3343762cfaaf..faf4956a0273 100644
--- a/mypy/test/testdeps.py
+++ b/mypy/test/testdeps.py
@@ -41,16 +41,9 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 a = ["Unknown compile error (likely syntax error in test case or fixture)"]
         else:
             deps: defaultdict[str, set[str]] = defaultdict(set)
-            for module in files:
-                if (
-                    module in dumped_modules
-                    or dump_all
-                    and module
-                    not in ("abc", "typing", "mypy_extensions", "typing_extensions", "enum")
-                ):
-                    new_deps = get_dependencies(
-                        files[module], type_map, options.python_version, options
-                    )
+            for module, file in files.items():
+                if (module in dumped_modules or dump_all) and (module in testcase.test_modules):
+                    new_deps = get_dependencies(file, type_map, options.python_version, options)
                     for source in new_deps:
                         deps[source].update(new_deps[source])
 
diff --git a/mypy/test/testmerge.py b/mypy/test/testmerge.py
index 595aba49d8b7..11e9a3c3d7e7 100644
--- a/mypy/test/testmerge.py
+++ b/mypy/test/testmerge.py
@@ -36,18 +36,6 @@
 AST = "AST"
 
 
-NOT_DUMPED_MODULES = (
-    "builtins",
-    "typing",
-    "abc",
-    "contextlib",
-    "sys",
-    "mypy_extensions",
-    "typing_extensions",
-    "enum",
-)
-
-
 class ASTMergeSuite(DataSuite):
     files = ["merge.test"]
 
@@ -84,13 +72,13 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
         target_path = os.path.join(test_temp_dir, "target.py")
         shutil.copy(os.path.join(test_temp_dir, "target.py.next"), target_path)
 
-        a.extend(self.dump(fine_grained_manager, kind))
+        a.extend(self.dump(fine_grained_manager, kind, testcase.test_modules))
         old_subexpr = get_subexpressions(result.manager.modules["target"])
 
         a.append("==>")
 
         new_file, new_types = self.build_increment(fine_grained_manager, "target", target_path)
-        a.extend(self.dump(fine_grained_manager, kind))
+        a.extend(self.dump(fine_grained_manager, kind, testcase.test_modules))
 
         for expr in old_subexpr:
             if isinstance(expr, TypeVarExpr):
@@ -137,8 +125,12 @@ def build_increment(
         type_map = manager.graph[module_id].type_map()
         return module, type_map
 
-    def dump(self, manager: FineGrainedBuildManager, kind: str) -> list[str]:
-        modules = manager.manager.modules
+    def dump(
+        self, manager: FineGrainedBuildManager, kind: str, test_modules: list[str]
+    ) -> list[str]:
+        modules = {
+            name: file for name, file in manager.manager.modules.items() if name in test_modules
+        }
         if kind == AST:
             return self.dump_asts(modules)
         elif kind == TYPEINFO:
@@ -146,15 +138,12 @@ def dump(self, manager: FineGrainedBuildManager, kind: str) -> list[str]:
         elif kind == SYMTABLE:
             return self.dump_symbol_tables(modules)
         elif kind == TYPES:
-            return self.dump_types(manager)
+            return self.dump_types(modules, manager)
         assert False, f"Invalid kind {kind}"
 
     def dump_asts(self, modules: dict[str, MypyFile]) -> list[str]:
         a = []
         for m in sorted(modules):
-            if m in NOT_DUMPED_MODULES:
-                # We don't support incremental checking of changes to builtins, etc.
-                continue
             s = modules[m].accept(self.str_conv)
             a.extend(s.splitlines())
         return a
@@ -162,9 +151,6 @@ def dump_asts(self, modules: dict[str, MypyFile]) -> list[str]:
     def dump_symbol_tables(self, modules: dict[str, MypyFile]) -> list[str]:
         a = []
         for id in sorted(modules):
-            if not is_dumped_module(id):
-                # We don't support incremental checking of changes to builtins, etc.
-                continue
             a.extend(self.dump_symbol_table(id, modules[id].names))
         return a
 
@@ -197,8 +183,6 @@ def format_symbol_table_node(self, node: SymbolTableNode) -> str:
     def dump_typeinfos(self, modules: dict[str, MypyFile]) -> list[str]:
         a = []
         for id in sorted(modules):
-            if not is_dumped_module(id):
-                continue
             a.extend(self.dump_typeinfos_recursive(modules[id].names))
         return a
 
@@ -217,13 +201,13 @@ def dump_typeinfo(self, info: TypeInfo) -> list[str]:
         s = info.dump(str_conv=self.str_conv, type_str_conv=self.type_str_conv)
         return s.splitlines()
 
-    def dump_types(self, manager: FineGrainedBuildManager) -> list[str]:
+    def dump_types(
+        self, modules: dict[str, MypyFile], manager: FineGrainedBuildManager
+    ) -> list[str]:
         a = []
         # To make the results repeatable, we try to generate unique and
         # deterministic sort keys.
-        for module_id in sorted(manager.manager.modules):
-            if not is_dumped_module(module_id):
-                continue
+        for module_id in sorted(modules):
             all_types = manager.manager.all_types
             # Compute a module type map from the global type map
             tree = manager.graph[module_id].tree
@@ -242,7 +226,3 @@ def dump_types(self, manager: FineGrainedBuildManager) -> list[str]:
 
     def format_type(self, typ: Type) -> str:
         return typ.accept(self.type_str_conv)
-
-
-def is_dumped_module(id: str) -> bool:
-    return id not in NOT_DUMPED_MODULES and (not id.startswith("_") or id == "__main__")
diff --git a/mypy/test/testsemanal.py b/mypy/test/testsemanal.py
index 71ebc43df8c2..3276f21540df 100644
--- a/mypy/test/testsemanal.py
+++ b/mypy/test/testsemanal.py
@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import os.path
 import sys
 from typing import Dict
 
@@ -77,27 +76,9 @@ def test_semanal(testcase: DataDrivenTestCase) -> None:
             raise CompileError(a)
         # Include string representations of the source files in the actual
         # output.
-        for fnam in sorted(result.files.keys()):
-            f = result.files[fnam]
-            # Omit the builtins module and files with a special marker in the
-            # path.
-            # TODO the test is not reliable
-            if (
-                not f.path.endswith(
-                    (
-                        os.sep + "builtins.pyi",
-                        "typing.pyi",
-                        "mypy_extensions.pyi",
-                        "typing_extensions.pyi",
-                        "abc.pyi",
-                        "collections.pyi",
-                        "sys.pyi",
-                    )
-                )
-                and not os.path.basename(f.path).startswith("_")
-                and not os.path.splitext(os.path.basename(f.path))[0].endswith("_")
-            ):
-                a += str(f).split("\n")
+        for module in sorted(result.files.keys()):
+            if module in testcase.test_modules:
+                a += str(result.files[module]).split("\n")
     except CompileError as e:
         a = e.messages
     if testcase.normalize_output:
@@ -164,10 +145,10 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
             a = result.errors
             if a:
                 raise CompileError(a)
-            for f in sorted(result.files.keys()):
-                if f not in ("builtins", "typing", "abc"):
-                    a.append(f"{f}:")
-                    for s in str(result.files[f].names).split("\n"):
+            for module in sorted(result.files.keys()):
+                if module in testcase.test_modules:
+                    a.append(f"{module}:")
+                    for s in str(result.files[module].names).split("\n"):
                         a.append("  " + s)
         except CompileError as e:
             a = e.messages
@@ -199,11 +180,13 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
 
             # Collect all TypeInfos in top-level modules.
             typeinfos = TypeInfoMap()
-            for f in result.files.values():
-                for n in f.names.values():
-                    if isinstance(n.node, TypeInfo):
-                        assert n.fullname
-                        typeinfos[n.fullname] = n.node
+            for module, file in result.files.items():
+                if module in testcase.test_modules:
+                    for n in file.names.values():
+                        if isinstance(n.node, TypeInfo):
+                            assert n.fullname
+                            if any(n.fullname.startswith(m + ".") for m in testcase.test_modules):
+                                typeinfos[n.fullname] = n.node
 
             # The output is the symbol table converted into a string.
             a = str(typeinfos).split("\n")
@@ -220,12 +203,7 @@ class TypeInfoMap(Dict[str, TypeInfo]):
     def __str__(self) -> str:
         a: list[str] = ["TypeInfoMap("]
         for x, y in sorted(self.items()):
-            if (
-                not x.startswith("builtins.")
-                and not x.startswith("typing.")
-                and not x.startswith("abc.")
-            ):
-                ti = ("\n" + "  ").join(str(y).split("\n"))
-                a.append(f"  {x} : {ti}")
+            ti = ("\n" + "  ").join(str(y).split("\n"))
+            a.append(f"  {x} : {ti}")
         a[-1] += ")"
         return "\n".join(a)
diff --git a/mypy/test/testtransform.py b/mypy/test/testtransform.py
index 1d3d4468444e..c765bae12062 100644
--- a/mypy/test/testtransform.py
+++ b/mypy/test/testtransform.py
@@ -2,8 +2,6 @@
 
 from __future__ import annotations
 
-import os.path
-
 from mypy import build
 from mypy.errors import CompileError
 from mypy.modulefinder import BuildSource
@@ -50,29 +48,12 @@ def test_transform(testcase: DataDrivenTestCase) -> None:
             raise CompileError(a)
         # Include string representations of the source files in the actual
         # output.
-        for fnam in sorted(result.files.keys()):
-            f = result.files[fnam]
-
-            # Omit the builtins module and files with a special marker in the
-            # path.
-            # TODO the test is not reliable
-            if (
-                not f.path.endswith(
-                    (
-                        os.sep + "builtins.pyi",
-                        "typing_extensions.pyi",
-                        "typing.pyi",
-                        "abc.pyi",
-                        "sys.pyi",
-                    )
-                )
-                and not os.path.basename(f.path).startswith("_")
-                and not os.path.splitext(os.path.basename(f.path))[0].endswith("_")
-            ):
+        for module in sorted(result.files.keys()):
+            if module in testcase.test_modules:
                 t = TypeAssertTransformVisitor()
                 t.test_only = True
-                f = t.mypyfile(f)
-                a += str(f).split("\n")
+                file = t.mypyfile(result.files[module])
+                a += str(file).split("\n")
     except CompileError as e:
         a = e.messages
     if testcase.normalize_output:
diff --git a/mypy/test/testtypegen.py b/mypy/test/testtypegen.py
index 22ef4272e933..3f09254f081a 100644
--- a/mypy/test/testtypegen.py
+++ b/mypy/test/testtypegen.py
@@ -48,6 +48,7 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
             # to simplify output.
             searcher = SkippedNodeSearcher()
             for file in result.files.values():
+                searcher.ignore_file = file.fullname not in testcase.test_modules
                 file.accept(searcher)
             ignored = searcher.nodes
 
diff --git a/mypy/test/visitors.py b/mypy/test/visitors.py
index 771119dbdc70..2b748ec1bdc4 100644
--- a/mypy/test/visitors.py
+++ b/mypy/test/visitors.py
@@ -8,15 +8,7 @@
 
 from __future__ import annotations
 
-from mypy.nodes import (
-    AssignmentStmt,
-    CallExpr,
-    Expression,
-    IntExpr,
-    MypyFile,
-    NameExpr,
-    TypeVarExpr,
-)
+from mypy.nodes import AssignmentStmt, CallExpr, Expression, IntExpr, NameExpr, Node, TypeVarExpr
 from mypy.traverser import TraverserVisitor
 from mypy.treetransform import TransformVisitor
 from mypy.types import Type
@@ -25,12 +17,8 @@
 # from testtypegen
 class SkippedNodeSearcher(TraverserVisitor):
     def __init__(self) -> None:
-        self.nodes: set[Expression] = set()
-        self.is_typing = False
-
-    def visit_mypy_file(self, f: MypyFile) -> None:
-        self.is_typing = f.fullname == "typing" or f.fullname == "builtins"
-        super().visit_mypy_file(f)
+        self.nodes: set[Node] = set()
+        self.ignore_file = False
 
     def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
         if s.type or ignore_node(s.rvalue):
@@ -40,14 +28,14 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
         super().visit_assignment_stmt(s)
 
     def visit_name_expr(self, n: NameExpr) -> None:
-        self.skip_if_typing(n)
+        if self.ignore_file:
+            self.nodes.add(n)
+        super().visit_name_expr(n)
 
     def visit_int_expr(self, n: IntExpr) -> None:
-        self.skip_if_typing(n)
-
-    def skip_if_typing(self, n: Expression) -> None:
-        if self.is_typing:
+        if self.ignore_file:
             self.nodes.add(n)
+        super().visit_int_expr(n)
 
 
 def ignore_node(node: Expression) -> bool:
diff --git a/test-data/unit/README.md b/test-data/unit/README.md
index 6cf0b1bb26cf..97680c949bef 100644
--- a/test-data/unit/README.md
+++ b/test-data/unit/README.md
@@ -36,7 +36,7 @@ the error message
 - `W: ...` and `N: ...` works exactly like `E: ...`, but report a warning and a note respectively
 - lines that don't contain the above should cause no type check errors
 - optional `[builtins fixtures/...]` tells the type checker to use
-stubs from the indicated file (see Fixtures section below)
+`builtins` stubs from the indicated file (see Fixtures section below)
 - optional `[out]` is an alternative to the `# E: ` notation: it indicates that
 any text after it contains the expected type checking error messages.
 Usually, `# E: ` is preferred because it makes it easier to associate the
@@ -65,7 +65,7 @@ Where the stubs for builtins come from for a given test:
 - The builtins used by default in unit tests live in
   `test-data/unit/lib-stub`.
 
-- Individual test cases can override the builtins stubs by using
+- Individual test cases can override the `builtins` stubs by using
   `[builtins fixtures/foo.pyi]`; this targets files in `test-data/unit/fixtures`.
   Feel free to modify existing files there or create new ones as you deem fit.
 
@@ -77,6 +77,21 @@ Where the stubs for builtins come from for a given test:
   addition with other mypy developers, as additions could slow down the test
   suite.
 
+- Some tests choose to customize the standard library in a way that's local to the test:
+  ```
+  [case testFoo]
+  ...
+  [file builtins.py]
+  class int:
+    def next_fibonacci() -> int: pass
+  ```
+  Another possible syntax is:
+  ```
+  [fixture builtins.py]
+  ```
+  Whether you use `[file ...]` or `[fixture ...]` depends on whether you want
+  the file to be part of the tested corpus (e.g. contribute to `[out]` section)
+  or only support the test.
 
 Running tests and linting
 -------------------------
diff --git a/test-data/unit/check-typeddict.test b/test-data/unit/check-typeddict.test
index e3d6188b643b..970dc05b488d 100644
--- a/test-data/unit/check-typeddict.test
+++ b/test-data/unit/check-typeddict.test
@@ -9,7 +9,7 @@ reveal_type(p)  # N: Revealed type is "TypedDict('__main__.Point', {'x': builtin
 reveal_type(p.values()) # N: Revealed type is "typing.Iterable[builtins.object]"
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
-[targets sys, __main__]
+[targets __main__]
 
 [case testCanCreateTypedDictInstanceWithDictCall]
 from mypy_extensions import TypedDict
diff --git a/test-data/unit/deps-types.test b/test-data/unit/deps-types.test
index 1d7064cde0c7..def117fe04df 100644
--- a/test-data/unit/deps-types.test
+++ b/test-data/unit/deps-types.test
@@ -852,8 +852,6 @@ class I: pass
 <mod.I.__new__> -> a
 <mod.I> -> <m.P>, a, mod.I
 <mod> -> a
-<sys.platform> -> sys
-<sys.version_info> -> sys
 
 [case testAliasDepsClassInFunction]
 from mod import I
diff --git a/test-data/unit/merge.test b/test-data/unit/merge.test
index 144a095440f2..42d38c89482c 100644
--- a/test-data/unit/merge.test
+++ b/test-data/unit/merge.test
@@ -1086,7 +1086,7 @@ a: A
 [file target.py.next]
 from _x import A
 a: A
-[file _x.pyi]
+[fixture _x.pyi]
 from typing import Generic, TypeVar, overload
 
 T = TypeVar('T')
diff --git a/test-data/unit/semanal-modules.test b/test-data/unit/semanal-modules.test
index bc381293161f..116747ae5cb9 100644
--- a/test-data/unit/semanal-modules.test
+++ b/test-data/unit/semanal-modules.test
@@ -77,9 +77,9 @@ MypyFile:1(
 [case testImportMultiple]
 import _m, _n
 _m.x, _n.y
-[file _m.py]
+[fixture _m.py]
 x = 1
-[file _n.py]
+[fixture _n.py]
 y = 2
 [out]
 MypyFile:1(
@@ -96,7 +96,7 @@ MypyFile:1(
 [case testImportAs]
 import _m as n
 n.x
-[file _m.py]
+[fixture _m.py]
 x = 1
 [out]
 MypyFile:1(
@@ -109,7 +109,7 @@ MypyFile:1(
 [case testImportFromMultiple]
 from _m import x, y
 x, y
-[file _m.py]
+[fixture _m.py]
 x = y = 1
 [out]
 MypyFile:1(
@@ -122,7 +122,7 @@ MypyFile:1(
 [case testImportFromAs]
 from _m import y as z
 z
-[file _m.py]
+[fixture _m.py]
 y = 1
 [out]
 MypyFile:1(
@@ -135,7 +135,7 @@ from m import x
 y = x
 [file m.py]
 from _n import x
-[file _n.py]
+[fixture _n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -150,9 +150,9 @@ MypyFile:1(
 [case testAccessImportedName2]
 import _m
 y = _m.x
-[file _m.py]
+[fixture _m.py]
 from _n import x
-[file _n.py]
+[fixture _n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -166,9 +166,9 @@ MypyFile:1(
 [case testAccessingImportedNameInType]
 from _m import c
 x = None # type: c
-[file _m.py]
+[fixture _m.py]
 from _n import c
-[file _n.py]
+[fixture _n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -181,9 +181,9 @@ MypyFile:1(
 [case testAccessingImportedNameInType2]
 import _m
 x = None # type: _m.c
-[file _m.py]
+[fixture _m.py]
 from _n import c
-[file _n.py]
+[fixture _n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -196,9 +196,9 @@ MypyFile:1(
 [case testAccessingImportedModule]
 from _m import _n
 _n.x
-[file _m.py]
+[fixture _m.py]
 import _n
-[file _n.py]
+[fixture _n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -211,9 +211,9 @@ MypyFile:1(
 [case testAccessingImportedModule2]
 import _m
 _m._n.x
-[file _m.py]
+[fixture _m.py]
 import _n
-[file _n.py]
+[fixture _n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -228,9 +228,9 @@ MypyFile:1(
 [case testAccessTypeViaDoubleIndirection]
 from _m import c
 a = None # type: c
-[file _m.py]
+[fixture _m.py]
 from _n import c
-[file _n.py]
+[fixture _n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -243,9 +243,9 @@ MypyFile:1(
 [case testAccessTypeViaDoubleIndirection2]
 import _m
 a = None # type: _m.c
-[file _m.py]
+[fixture _m.py]
 from _n import c
-[file _n.py]
+[fixture _n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -258,7 +258,7 @@ MypyFile:1(
 [case testImportAsterisk]
 from _m import *
 x, y
-[file _m.py]
+[fixture _m.py]
 x = y = 1
 [out]
 MypyFile:1(
@@ -271,10 +271,10 @@ MypyFile:1(
 [case testImportAsteriskAndImportedNames]
 from _m import *
 n_.x, y
-[file _m.py]
+[fixture _m.py]
 import n_
 from n_ import y
-[file n_.py]
+[fixture n_.py]
 x = y = 1
 [out]
 MypyFile:1(
@@ -290,10 +290,10 @@ MypyFile:1(
 from _m import *
 x = None # type: n_.c
 y = None # type: d
-[file _m.py]
+[fixture _m.py]
 import n_
 from n_ import d
-[file n_.py]
+[fixture n_.py]
 class c: pass
 class d: pass
 [out]
@@ -311,7 +311,7 @@ MypyFile:1(
 [case testModuleInSubdir]
 import _m
 _m.x
-[file _m/__init__.py]
+[fixture _m/__init__.py]
 x = 1
 [out]
 MypyFile:1(
@@ -324,7 +324,7 @@ MypyFile:1(
 [case testNestedModules]
 import m.n
 m.n.x, m.y
-[file m/__init__.py]
+[fixture m/__init__.py]
 y = 1
 [file m/n.py]
 x = 1
@@ -351,8 +351,8 @@ MypyFile:1(
 [case testImportFromSubmodule]
 from m._n import x
 x
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -363,8 +363,8 @@ MypyFile:1(
 [case testImportAllFromSubmodule]
 from m._n import *
 x, y
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 x = y = 1
 [out]
 MypyFile:1(
@@ -377,8 +377,8 @@ MypyFile:1(
 [case testSubmodulesAndTypes]
 import m._n
 x = None # type: m._n.c
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -391,8 +391,8 @@ MypyFile:1(
 [case testSubmodulesAndTypes2]
 from m._n import c
 x = None # type: c
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 class c: pass
 [out]
 MypyFile:1(
@@ -405,8 +405,8 @@ MypyFile:1(
 [case testFromPackageImportModule]
 from m import _n
 _n.x
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 x = 1
 [out]
 MypyFile:1(
@@ -421,9 +421,9 @@ import m.n.k
 m.n.k.x
 m.n.b
 m.a
-[file m/__init__.py]
+[fixture m/__init__.py]
 a = 1
-[file m/n/__init__.py]
+[fixture m/n/__init__.py]
 b = 1
 [file m/n/k.py]
 x = 1
@@ -458,10 +458,10 @@ MypyFile:1(
 [case testImportInSubmodule]
 import m._n
 y = m._n.x
-[file m/__init__.py]
-[file m/_n.py]
+[fixture m/__init__.py]
+[fixture m/_n.py]
 from m._k import x
-[file m/_k.py]
+[fixture m/_k.py]
 x = 1
 [out]
 MypyFile:1(
@@ -494,7 +494,7 @@ MypyFile:1(
 import _m
 _m.x = (
   _m.x)
-[file _m.py]
+[fixture _m.py]
 x = None
 [out]
 MypyFile:1(
@@ -510,7 +510,7 @@ MypyFile:1(
 [case testAssignmentThatRefersToModule]
 import _m
 _m.x[None] = None
-[file _m.py]
+[fixture _m.py]
 x = None
 [out]
 MypyFile:1(
@@ -527,7 +527,7 @@ MypyFile:1(
 if 1:
     import _x
     _x.y
-[file _x.py]
+[fixture _x.py]
 y = 1
 [out]
 MypyFile:1(
@@ -545,7 +545,7 @@ MypyFile:1(
 def f() -> None:
     import _x
     _x.y
-[file _x.py]
+[fixture _x.py]
 y = 1
 [out]
 MypyFile:1(
@@ -563,7 +563,7 @@ MypyFile:1(
 class A:
     from _x import y
     z = y
-[file _x.py]
+[fixture _x.py]
 y = 1
 [out]
 MypyFile:1(
@@ -578,7 +578,7 @@ MypyFile:1(
 class A:
     import _x
     z = _x.y
-[file _x.py]
+[fixture _x.py]
 y = 1
 [out]
 MypyFile:1(
@@ -620,7 +620,7 @@ MypyFile:1(
 [case testRelativeImport0]
 import m.x
 m.x.z.y
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 from . import z
 [file m/z.py]
@@ -650,12 +650,12 @@ MypyFile:1(
 import m.t.b as b
 b.x.y
 b.z.y
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 y = 1
 [file m/z.py]
 y = 3
-[file m/t/__init__.py]
+[fixture m/t/__init__.py]
 [file m/t/b.py]
 from .. import x, z
 [out]
@@ -693,12 +693,12 @@ MypyFile:1(
 import m.t.b as b
 b.xy
 b.zy
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 y = 1
 [file m/z.py]
 y = 3
-[file m/t/__init__.py]
+[fixture m/t/__init__.py]
 [file m/t/b.py]
 from ..x import y as xy
 from ..z import y as zy
@@ -735,14 +735,14 @@ import m.t
 m.zy
 m.xy
 m.t.y
-[file m/__init__.py]
+[fixture m/__init__.py]
 from .x import *
 from .z import *
 [file m/x.py]
 from .z import zy as xy
 [file m/z.py]
 zy = 3
-[file m/t/__init__.py]
+[fixture m/t/__init__.py]
 from .b import *
 [file m/t/b.py]
 from .. import xy as y
@@ -778,7 +778,7 @@ MypyFile:1(
 
 [case testRelativeImportFromSameModule]
 import m.x
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 from .x import nonexistent
 [out]
@@ -786,7 +786,7 @@ tmp/m/x.py:1: error: Module "m.x" has no attribute "nonexistent"
 
 [case testImportFromSameModule]
 import m.x
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 from m.x import nonexistent
 [out]
@@ -794,7 +794,7 @@ tmp/m/x.py:1: error: Module "m.x" has no attribute "nonexistent"
 
 [case testImportMisspellingSingleCandidate]
 import f
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 def some_function():
     pass
@@ -805,7 +805,7 @@ tmp/f.py:1: error: Module "m.x" has no attribute "somefunction"; maybe "some_fun
 
 [case testImportMisspellingMultipleCandidates]
 import f
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 def some_function():
     pass
@@ -818,7 +818,7 @@ tmp/f.py:1: error: Module "m.x" has no attribute "somefunction"; maybe "some_fun
 
 [case testImportMisspellingMultipleCandidatesTruncated]
 import f
-[file m/__init__.py]
+[fixture m/__init__.py]
 [file m/x.py]
 def some_function():
     pass
@@ -849,10 +849,10 @@ y = 2
 from m_ import *
 x
 y
-[file m_.py]
+[fixture m_.py]
 from m2_ import x as x
 from m2_ import y
-[file m2_.py]
+[fixture m2_.py]
 x = 1
 y = 2
 [out]
@@ -878,11 +878,11 @@ import m3
 from m_ import *
 m2_
 m3_
-[file m_.py]
+[fixture m_.py]
 import m2_ as m2_
 import m3_
-[file m2_.py]
-[file m3_.py]
+[fixture m2_.py]
+[fixture m3_.py]
 [out]
 MypyFile:1(
   ImportAll:1(m_)
diff --git a/test-data/unit/semanal-python310.test b/test-data/unit/semanal-python310.test
index 9418ac2912b2..e96a3ca9d777 100644
--- a/test-data/unit/semanal-python310.test
+++ b/test-data/unit/semanal-python310.test
@@ -194,7 +194,7 @@ x = 1
 match x:
     case _a.b:
         pass
-[file _a.py]
+[fixture _a.py]
 b = 1
 [out]
 MypyFile:1(
diff --git a/test-data/unit/semanal-symtable.test b/test-data/unit/semanal-symtable.test
index c886080557b0..1622fd1f1ad4 100644
--- a/test-data/unit/semanal-symtable.test
+++ b/test-data/unit/semanal-symtable.test
@@ -78,10 +78,6 @@ __main__:
     non_existing2 : Gdef/Var (__main__.non_existing2) : Any
     non_existing3 : Gdef/Var (__main__.non_existing3) : Any
     non_existing4 : Gdef/Var (__main__.non_existing4) : Any)
-sys:
-  SymbolTable(
-    platform : Gdef/Var (sys.platform) : builtins.str
-    version_info : Gdef/Var (sys.version_info))
 
 [case testDecorator]
 from typing import Callable
diff --git a/test-data/unit/semanal-typealiases.test b/test-data/unit/semanal-typealiases.test
index debc7ecdf722..88d234134350 100644
--- a/test-data/unit/semanal-typealiases.test
+++ b/test-data/unit/semanal-typealiases.test
@@ -92,7 +92,7 @@ import typing
 import _m
 A2 = _m.A
 x = 1 # type: A2
-[file _m.py]
+[fixture _m.py]
 import typing
 class A: pass
 [out]
@@ -255,7 +255,7 @@ MypyFile:1(
 import typing
 from _m import U
 def f(x: U) -> None: pass
-[file _m.py]
+[fixture _m.py]
 from typing import Union
 class A: pass
 U = Union[int, A]
@@ -275,7 +275,7 @@ MypyFile:1(
 import typing
 import _m
 def f(x: _m.U) -> None: pass
-[file _m.py]
+[fixture _m.py]
 from typing import Union
 class A: pass
 U = Union[int, A]
@@ -295,7 +295,7 @@ MypyFile:1(
 import typing
 from _m import A
 def f(x: A) -> None: pass
-[file _m.py]
+[fixture _m.py]
 import typing
 A = int
 [out]
@@ -314,7 +314,7 @@ MypyFile:1(
 import typing
 import _m
 def f(x: _m.A) -> None: pass
-[file _m.py]
+[fixture _m.py]
 import typing
 A = int
 [out]
@@ -385,7 +385,7 @@ from typing import Union
 from _m import U
 U2 = U
 x = 1 # type: U2
-[file _m.py]
+[fixture _m.py]
 from typing import Union
 U = Union[int, str]
 [out]
diff --git a/test-data/unit/semanal-types.test b/test-data/unit/semanal-types.test
index 494d701b758a..05fc08d8a49e 100644
--- a/test-data/unit/semanal-types.test
+++ b/test-data/unit/semanal-types.test
@@ -303,7 +303,7 @@ MypyFile:1(
 import typing
 import _m
 typing.cast(_m.C, object)
-[file _m.py]
+[fixture _m.py]
 class C: pass
 [out]
 MypyFile:1(
@@ -318,8 +318,8 @@ MypyFile:1(
 import typing
 import _m._n
 typing.cast(_m._n.C, object)
-[file _m/__init__.py]
-[file _m/_n.py]
+[fixture _m/__init__.py]
+[fixture _m/_n.py]
 class C: pass
 [out]
 MypyFile:1(
@@ -1152,7 +1152,7 @@ from typing import Generic
 from _m import T
 class A(Generic[T]):
     y = None # type: T
-[file _m.py]
+[fixture _m.py]
 from typing import TypeVar
 T = TypeVar('T')
 [out]
@@ -1175,7 +1175,7 @@ class A(Generic[_m.T]):
     a = None # type: _m.T
     def f(self, x: _m.T):
         b = None # type: _m.T
-[file _m.py]
+[fixture _m.py]
 from typing import TypeVar
 T = TypeVar('T')
 [out]
@@ -1206,7 +1206,7 @@ MypyFile:1(
 import _m
 def f(x: _m.T) -> None:
     a = None # type: _m.T
-[file _m.py]
+[fixture _m.py]
 from typing import TypeVar
 T = TypeVar('T')
 [out]