diff --git a/mypy/test/data.py b/mypy/test/data.py
index 5edc68f78a88..717ebdc9ebb2 100644
--- a/mypy/test/data.py
+++ b/mypy/test/data.py
@@ -207,6 +207,16 @@ def parse_test_case(case: DataDrivenTestCase) -> None:
     for file_path, contents in files:
         expand_errors(contents.split("\n"), output, file_path)
 
+    seen_files = set()
+    for file, _ in files:
+        if file in seen_files:
+            raise ValueError(
+                f"{case.file}, line {first_item.line}: Duplicated filename {file}. Did you include"
+                " it multiple times?"
+            )
+
+        seen_files.add(file)
+
     case.input = input
     case.output = output
     case.output2 = output2
diff --git a/test-data/unit/check-attr.test b/test-data/unit/check-attr.test
index 89eab92ebabd..3ca804943010 100644
--- a/test-data/unit/check-attr.test
+++ b/test-data/unit/check-attr.test
@@ -1714,8 +1714,6 @@ class C:
     # Note that for this test, the 'Value of type "int" is not indexable' errors are silly,
     # and a consequence of Callable etc. being set to an int in the test stub.
     b = attr.ib(type=Callable[[], C])
-[builtins fixtures/bool.pyi]
-
 [file b.py]
 import attr
 import a
diff --git a/test-data/unit/check-enum.test b/test-data/unit/check-enum.test
index 80a7ca7ff99f..b62ed3d94210 100644
--- a/test-data/unit/check-enum.test
+++ b/test-data/unit/check-enum.test
@@ -1345,7 +1345,6 @@ class Foo(bytes, Enum):
 a = Foo.A
 reveal_type(a.value)    # N: Revealed type is "Any"
 reveal_type(a._value_)  # N: Revealed type is "Any"
-[builtins fixtures/__new__.pyi]
 [builtins fixtures/primitives.pyi]
 [typing fixtures/typing-medium.pyi]
 
@@ -1368,7 +1367,6 @@ class Bar(Foo):
 a = Bar.A
 reveal_type(a.value)    # N: Revealed type is "Any"
 reveal_type(a._value_)  # N: Revealed type is "Any"
-[builtins fixtures/__new__.pyi]
 [builtins fixtures/primitives.pyi]
 [typing fixtures/typing-medium.pyi]
 
diff --git a/test-data/unit/check-functools.test b/test-data/unit/check-functools.test
index f95b823a5291..ebfe86f2b241 100644
--- a/test-data/unit/check-functools.test
+++ b/test-data/unit/check-functools.test
@@ -20,7 +20,6 @@ Ord() <= 1  # E: Unsupported operand types for <= ("Ord" and "int")
 Ord() == 1
 Ord() > 1  # E: Unsupported operand types for > ("Ord" and "int")
 Ord() >= 1  # E: Unsupported operand types for >= ("Ord" and "int")
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testTotalOrderingLambda]
@@ -43,7 +42,6 @@ Ord() <= 1  # E: Unsupported operand types for <= ("Ord" and "int")
 Ord() == 1
 Ord() > 1  # E: Unsupported operand types for > ("Ord" and "int")
 Ord() >= 1  # E: Unsupported operand types for >= ("Ord" and "int")
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testTotalOrderingNonCallable]
@@ -59,8 +57,6 @@ class Ord(object):
 Ord() <= Ord()  # E: Unsupported left operand type for <= ("Ord")
 Ord() > Ord()  # E: "int" not callable
 Ord() >= Ord()  # E: Unsupported left operand type for >= ("Ord")
-
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testTotalOrderingReturnNotBool]
@@ -79,8 +75,6 @@ reveal_type(Ord() <= Ord())  # N: Revealed type is "Any"
 reveal_type(Ord() == Ord())  # N: Revealed type is "builtins.bool"
 reveal_type(Ord() > Ord())  # N: Revealed type is "Any"
 reveal_type(Ord() >= Ord())  # N: Revealed type is "Any"
-
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testTotalOrderingAllowsAny]
@@ -105,7 +99,6 @@ Ord() <= 1  # E: Unsupported left operand type for <= ("Ord")
 Ord() == 1
 Ord() > 1
 Ord() >= 1  # E: Unsupported left operand type for >= ("Ord")
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testCachedProperty]
@@ -151,5 +144,4 @@ def f(d: D[C]) -> None:
     reveal_type(d.__gt__)  # N: Revealed type is "def (other: Any) -> builtins.bool"
 
 d: D[int]  # E: Type argument "int" of "D" must be a subtype of "C"
-[builtins fixtures/ops.pyi]
 [builtins fixtures/dict.pyi]
diff --git a/test-data/unit/check-isinstance.test b/test-data/unit/check-isinstance.test
index 0722ee8d91e5..2d010b8ba38d 100644
--- a/test-data/unit/check-isinstance.test
+++ b/test-data/unit/check-isinstance.test
@@ -2670,10 +2670,9 @@ if type(x) == int == str:
 else:
     reveal_type(x)  # N: Revealed type is "Union[builtins.int, builtins.str]"
 
-# mypy shows an error about "Unsupported left operand type for !=" if we don't include this
-[builtins fixtures/typing-medium.pyi]
 # mypy thinks int isn't defined unless we include this
 [builtins fixtures/primitives.pyi]
+
 [case testTypeNotEqualsCheck]
 from typing import Union
 
@@ -2683,8 +2682,6 @@ if type(x) != int:
 else:
     reveal_type(x)  # N: Revealed type is "builtins.int"
 
-# mypy shows an error about "Unsupported left operand type for !=" if we don't include this
-[builtins fixtures/typing-medium.pyi]
 # mypy thinks int isn't defined unless we include this
 [builtins fixtures/primitives.pyi]
 
diff --git a/test-data/unit/check-modules.test b/test-data/unit/check-modules.test
index 4b8308310ae6..1bf0e4874926 100644
--- a/test-data/unit/check-modules.test
+++ b/test-data/unit/check-modules.test
@@ -3216,7 +3216,6 @@ class Bar(Foo):
 from a import Foo
 class Bar(Foo):
     def frobnicate(self, *args) -> None: pass # type: ignore[override] # I know
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 [out1]
 tmp/b.py:3: error: Signature of "frobnicate" incompatible with supertype "Foo"
diff --git a/test-data/unit/check-parameter-specification.test b/test-data/unit/check-parameter-specification.test
index 7ef0485f7841..fe66b18fbfea 100644
--- a/test-data/unit/check-parameter-specification.test
+++ b/test-data/unit/check-parameter-specification.test
@@ -539,7 +539,6 @@ def three(**kwargs: int) -> int: ...
 
 @expects_int_first # Accepted
 def four(*args: int) -> int: ...
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testParamSpecTwiceSolving]
diff --git a/test-data/unit/check-protocols.test b/test-data/unit/check-protocols.test
index 3b8e668c7546..182745b99e40 100644
--- a/test-data/unit/check-protocols.test
+++ b/test-data/unit/check-protocols.test
@@ -2280,7 +2280,6 @@ def func2(arg: Optional[A]) -> None: ...
 x: B
 func1(x)
 func2(x)
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 [out]
 main:14: error: Argument 1 to "func1" has incompatible type "B"; expected "A"
@@ -3191,7 +3190,6 @@ class NoneCompatible3(Protocol):
 
 class C(NoneCompatible3): ...
 C() # E: Cannot instantiate abstract class "C" with abstract attributes "f", "g" and "h"
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/classmethod.pyi]
 
 [case testEmptyBodyWithFinal]
diff --git a/test-data/unit/check-singledispatch.test b/test-data/unit/check-singledispatch.test
index 8fe049437c57..45bf1ca9cbf2 100644
--- a/test-data/unit/check-singledispatch.test
+++ b/test-data/unit/check-singledispatch.test
@@ -180,9 +180,6 @@ def f(arg) -> None:
 @f.register
 def g(arg: Mapping) -> None:
     pass
-
-[builtins fixtures/args.pyi]
-[builtins fixtures/list.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testIncorrectArgumentsInSingledispatchFunctionDefinition]
diff --git a/test-data/unit/check-slots.test b/test-data/unit/check-slots.test
index 8beb0d8bf3f7..b7ce5e596101 100644
--- a/test-data/unit/check-slots.test
+++ b/test-data/unit/check-slots.test
@@ -26,7 +26,6 @@ class WithVariable:
         self.a = 1
         self.b = 2
         self.c = 3
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/list.pyi]
 
 
@@ -332,7 +331,6 @@ b.extra = 'extra'
 main:22: error: Trying to assign name "c" that is not in "__slots__" of type "__main__.B"
 main:43: error: Trying to assign name "c" that is not in "__slots__" of type "__main__.B"
 main:47: error: "B" has no attribute "extra"
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/property.pyi]
 
 
@@ -363,7 +361,6 @@ a.c = custom_obj
 a.d = custom_obj
 a.e = custom_obj
 [out]
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 
 
@@ -473,7 +470,6 @@ class A:
         self.a = 1
         self.b = 2
         self.missing = 3
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/list.pyi]
 
 
@@ -486,7 +482,6 @@ class A:
         self.a = 1
         self.b = 2
         self.missing = 3
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/set.pyi]
 
 
@@ -499,7 +494,6 @@ class A:
         self.a = 1
         self.b = 2
         self.missing = 3
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 
 
diff --git a/test-data/unit/check-typevar-values.test b/test-data/unit/check-typevar-values.test
index a4a4d68bd9fe..83340c52b63b 100644
--- a/test-data/unit/check-typevar-values.test
+++ b/test-data/unit/check-typevar-values.test
@@ -660,8 +660,6 @@ T = TypeVar("T", bound=Union[Data, Dict[str, str]])
 
 def f(data: T) -> None:
     reveal_type(data["x"]) # N: Revealed type is "Union[builtins.int, builtins.str]"
-
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testTypeVarWithTypedDictValueInIndexExpression]
@@ -677,7 +675,6 @@ T = TypeVar("T", Data, Dict[str, str])
 
 def f(data: T) -> None:
     _: Union[str, int] = data["x"]
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/dict.pyi]
 
 [case testSelfTypeVarIndexExpr]
@@ -699,8 +696,6 @@ class Indexable:
 
     def m(self: T) -> T:
         return self["foo"]
-
-[builtins fixtures/tuple.pyi]
 [builtins fixtures/classmethod.pyi]
 
 [case testTypeVarWithValueDeferral]
diff --git a/test-data/unit/fine-grained-modules.test b/test-data/unit/fine-grained-modules.test
index f76ced64341b..9b13d718bbe6 100644
--- a/test-data/unit/fine-grained-modules.test
+++ b/test-data/unit/fine-grained-modules.test
@@ -1806,7 +1806,7 @@ import b
 [file b.py]
 [file c.py]
 x = 1
-[file b.py]
+[file b.py.2]
 1+'x'
 [file c.py.2]
 x = '2'
diff --git a/test-data/unit/fine-grained.test b/test-data/unit/fine-grained.test
index 58339828677d..d32ae320ca64 100644
--- a/test-data/unit/fine-grained.test
+++ b/test-data/unit/fine-grained.test
@@ -989,7 +989,6 @@ import attr
 class A:
     a: int
     other: int
-[builtins fixtures/list.pyi]
 
 [file a.py.3]
 import attr