diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index 236b05e0598..6d03935ca1c 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -34,20 +34,22 @@ func mustParse(path, src string) *syntax.File {
 	return f
 }
 
-func typecheck(path, src string, info *Info) (*Package, error) {
+func typecheck(path, src string, conf *Config, info *Info) (*Package, error) {
 	f, err := parse(path, src)
 	if f == nil { // ignore errors unless f is nil
 		return nil, err
 	}
-	conf := Config{
-		Error:    func(err error) {}, // collect all errors
-		Importer: defaultImporter(),
+	if conf == nil {
+		conf = &Config{
+			Error:    func(err error) {}, // collect all errors
+			Importer: defaultImporter(),
+		}
 	}
 	return conf.Check(f.PkgName.Value, []*syntax.File{f}, info)
 }
 
-func mustTypecheck(path, src string, info *Info) *Package {
-	pkg, err := typecheck(path, src, info)
+func mustTypecheck(path, src string, conf *Config, info *Info) *Package {
+	pkg, err := typecheck(path, src, conf, info)
 	if err != nil {
 		panic(err) // so we don't need to pass *testing.T
 	}
@@ -137,7 +139,7 @@ func TestValuesInfo(t *testing.T) {
 		info := Info{
 			Types: make(map[syntax.Expr]TypeAndValue),
 		}
-		name := mustTypecheck("ValuesInfo", test.src, &info).Name()
+		name := mustTypecheck("ValuesInfo", test.src, nil, &info).Name()
 
 		// look for expression
 		var expr syntax.Expr
@@ -379,7 +381,7 @@ func TestTypesInfo(t *testing.T) {
 		info := Info{Types: make(map[syntax.Expr]TypeAndValue)}
 		var name string
 		if strings.HasPrefix(test.src, brokenPkg) {
-			pkg, err := typecheck("TypesInfo", test.src, &info)
+			pkg, err := typecheck("TypesInfo", test.src, nil, &info)
 			if err == nil {
 				t.Errorf("package %s: expected to fail but passed", pkg.Name())
 				continue
@@ -388,7 +390,7 @@ func TestTypesInfo(t *testing.T) {
 				name = pkg.Name()
 			}
 		} else {
-			name = mustTypecheck("TypesInfo", test.src, &info).Name()
+			name = mustTypecheck("TypesInfo", test.src, nil, &info).Name()
 		}
 
 		// look for expression type
@@ -553,8 +555,7 @@ type T[P any] []P
 		instMap := make(map[*syntax.Name]Instance)
 		useMap := make(map[*syntax.Name]Object)
 		makePkg := func(src string) *Package {
-			f := mustParse("p.go", src)
-			pkg, _ := conf.Check("", []*syntax.File{f}, &Info{Instances: instMap, Uses: useMap})
+			pkg, _ := typecheck("p.go", src, &conf, &Info{Instances: instMap, Uses: useMap})
 			imports[pkg.Name()] = pkg
 			return pkg
 		}
@@ -650,7 +651,7 @@ func TestDefsInfo(t *testing.T) {
 		info := Info{
 			Defs: make(map[*syntax.Name]Object),
 		}
-		name := mustTypecheck("DefsInfo", test.src, &info).Name()
+		name := mustTypecheck("DefsInfo", test.src, nil, &info).Name()
 
 		// find object
 		var def Object
@@ -715,7 +716,7 @@ func TestUsesInfo(t *testing.T) {
 		info := Info{
 			Uses: make(map[*syntax.Name]Object),
 		}
-		name := mustTypecheck("UsesInfo", test.src, &info).Name()
+		name := mustTypecheck("UsesInfo", test.src, nil, &info).Name()
 
 		// find object
 		var use Object
@@ -855,7 +856,7 @@ func TestImplicitsInfo(t *testing.T) {
 		info := Info{
 			Implicits: make(map[syntax.Node]Object),
 		}
-		name := mustTypecheck("ImplicitsInfo", test.src, &info).Name()
+		name := mustTypecheck("ImplicitsInfo", test.src, nil, &info).Name()
 
 		// the test cases expect at most one Implicits entry
 		if len(info.Implicits) > 1 {
@@ -983,7 +984,7 @@ func TestPredicatesInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{Types: make(map[syntax.Expr]TypeAndValue)}
-		name := mustTypecheck("PredicatesInfo", test.src, &info).Name()
+		name := mustTypecheck("PredicatesInfo", test.src, nil, &info).Name()
 
 		// look for expression predicates
 		got := "<missing>"
@@ -1075,7 +1076,7 @@ func TestScopesInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{Scopes: make(map[syntax.Node]*Scope)}
-		name := mustTypecheck("ScopesInfo", test.src, &info).Name()
+		name := mustTypecheck("ScopesInfo", test.src, nil, &info).Name()
 
 		// number of scopes must match
 		if len(info.Scopes) != len(test.scopes) {
@@ -1263,7 +1264,7 @@ func TestInitOrderInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{}
-		name := mustTypecheck("InitOrderInfo", test.src, &info).Name()
+		name := mustTypecheck("InitOrderInfo", test.src, nil, &info).Name()
 
 		// number of initializers must match
 		if len(info.InitOrder) != len(test.inits) {
@@ -1354,11 +1355,7 @@ func TestSelection(t *testing.T) {
 	imports := make(testImporter)
 	conf := Config{Importer: imports}
 	makePkg := func(path, src string) {
-		f := mustParse(path+".go", src)
-		pkg, err := conf.Check(path, []*syntax.File{f}, &Info{Selections: selections})
-		if err != nil {
-			t.Fatal(err)
-		}
+		pkg := mustTypecheck(path, src, &conf, &Info{Selections: selections})
 		imports[path] = pkg
 	}
 
@@ -1632,7 +1629,7 @@ func TestLookupFieldOrMethod(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck("test", "package p;"+test.src, nil)
+		pkg := mustTypecheck("test", "package p;"+test.src, nil, nil)
 
 		obj := pkg.Scope().Lookup("a")
 		if obj == nil {
@@ -1912,7 +1909,7 @@ func TestIdentical(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck("test", "package p;"+test.src, nil)
+		pkg := mustTypecheck("test", "package p;"+test.src, nil, nil)
 		X := pkg.Scope().Lookup("X")
 		Y := pkg.Scope().Lookup("Y")
 		if X == nil || Y == nil {
@@ -2187,7 +2184,7 @@ func f(x T) T { return foo.F(x) }
 func TestInstantiate(t *testing.T) {
 	// eventually we like more tests but this is a start
 	const src = "package p; type T[P any] *T[P]"
-	pkg := mustTypecheck(".", src, nil)
+	pkg := mustTypecheck(".", src, nil, nil)
 
 	// type T should have one type parameter
 	T := pkg.Scope().Lookup("T").Type().(*Named)
@@ -2222,7 +2219,7 @@ func TestInstantiateErrors(t *testing.T) {
 
 	for _, test := range tests {
 		src := "package p; " + test.src
-		pkg := mustTypecheck(".", src, nil)
+		pkg := mustTypecheck(".", src, nil, nil)
 
 		T := pkg.Scope().Lookup("T").Type().(*Named)
 
@@ -2542,7 +2539,7 @@ type V4 struct{}
 func (V4) M()
 `
 
-	pkg := mustTypecheck("p.go", src, nil)
+	pkg := mustTypecheck("p.go", src, nil, nil)
 
 	T := pkg.Scope().Lookup("T").Type().Underlying().(*Interface)
 	lookup := func(name string) (*Func, bool) {
diff --git a/src/cmd/compile/internal/types2/builtins_test.go b/src/cmd/compile/internal/types2/builtins_test.go
index 0d4f57e277f..c3647e69a41 100644
--- a/src/cmd/compile/internal/types2/builtins_test.go
+++ b/src/cmd/compile/internal/types2/builtins_test.go
@@ -173,20 +173,10 @@ func TestBuiltinSignatures(t *testing.T) {
 
 func testBuiltinSignature(t *testing.T, name, src0, want string) {
 	src := fmt.Sprintf(`package p; import "unsafe"; type _ unsafe.Pointer /* use unsafe */; func _[P ~[]byte]() { %s }`, src0)
-	f, err := parse("", src)
-	if err != nil {
-		t.Errorf("%s: %s", src0, err)
-		return
-	}
 
-	conf := Config{Importer: defaultImporter()}
 	uses := make(map[*syntax.Name]Object)
 	types := make(map[syntax.Expr]TypeAndValue)
-	_, err = conf.Check(f.PkgName.Value, []*syntax.File{f}, &Info{Uses: uses, Types: types})
-	if err != nil {
-		t.Errorf("%s: %s", src0, err)
-		return
-	}
+	mustTypecheck("p", src, nil, &Info{Uses: uses, Types: types})
 
 	// find called function
 	n := 0
diff --git a/src/cmd/compile/internal/types2/example_test.go b/src/cmd/compile/internal/types2/example_test.go
index b89cadfb4a2..9ff7d0cfa2e 100644
--- a/src/cmd/compile/internal/types2/example_test.go
+++ b/src/cmd/compile/internal/types2/example_test.go
@@ -119,8 +119,6 @@ func fib(x int) int {
 	}
 	return fib(x-1) - fib(x-2)
 }`
-	f := mustParse("fib.go", input)
-
 	// Type-check the package.
 	// We create an empty map for each kind of input
 	// we're interested in, and Check populates them.
@@ -129,11 +127,7 @@ func fib(x int) int {
 		Defs:  make(map[*syntax.Name]types2.Object),
 		Uses:  make(map[*syntax.Name]types2.Object),
 	}
-	var conf types2.Config
-	pkg, err := conf.Check("fib", []*syntax.File{f}, &info)
-	if err != nil {
-		log.Fatal(err)
-	}
+	pkg := mustTypecheck("fib.go", input, nil, &info)
 
 	// Print package-level variables in initialization order.
 	fmt.Printf("InitOrder: %v\n\n", info.InitOrder)
diff --git a/src/cmd/compile/internal/types2/hilbert_test.go b/src/cmd/compile/internal/types2/hilbert_test.go
index 0e9d4c3f5b7..8b7ceb3c971 100644
--- a/src/cmd/compile/internal/types2/hilbert_test.go
+++ b/src/cmd/compile/internal/types2/hilbert_test.go
@@ -25,7 +25,7 @@ func TestHilbert(t *testing.T) {
 		return
 	}
 
-	mustTypecheck("hilbert.go", string(src), nil)
+	mustTypecheck("hilbert.go", string(src), nil, nil)
 }
 
 func program(n int, out string) []byte {
diff --git a/src/cmd/compile/internal/types2/instantiate_test.go b/src/cmd/compile/internal/types2/instantiate_test.go
index 33a34d76f39..e809d17de13 100644
--- a/src/cmd/compile/internal/types2/instantiate_test.go
+++ b/src/cmd/compile/internal/types2/instantiate_test.go
@@ -107,7 +107,7 @@ func TestInstantiateEquality(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck(".", test.src, nil)
+		pkg := mustTypecheck(".", test.src, nil, nil)
 
 		t.Run(pkg.Name(), func(t *testing.T) {
 			ctxt := NewContext()
@@ -133,8 +133,8 @@ func TestInstantiateEquality(t *testing.T) {
 
 func TestInstantiateNonEquality(t *testing.T) {
 	const src = "package p; type T[P any] int"
-	pkg1 := mustTypecheck(".", src, nil)
-	pkg2 := mustTypecheck(".", src, nil)
+	pkg1 := mustTypecheck(".", src, nil, nil)
+	pkg2 := mustTypecheck(".", src, nil, nil)
 	// We consider T1 and T2 to be distinct types, so their instances should not
 	// be deduplicated by the context.
 	T1 := pkg1.Scope().Lookup("T").Type().(*Named)
@@ -179,7 +179,7 @@ var X T[int]
 
 	for _, test := range tests {
 		src := prefix + test.decl
-		pkg := mustTypecheck(".", src, nil)
+		pkg := mustTypecheck(".", src, nil, nil)
 		typ := NewPointer(pkg.Scope().Lookup("X").Type())
 		obj, _, _ := LookupFieldOrMethod(typ, false, pkg, "m")
 		m, _ := obj.(*Func)
@@ -201,7 +201,7 @@ func (T[P]) m() {}
 
 var _ T[int]
 `
-	pkg := mustTypecheck(".", src, nil)
+	pkg := mustTypecheck(".", src, nil, nil)
 	typ := pkg.Scope().Lookup("T").Type().(*Named)
 	obj, _, _ := LookupFieldOrMethod(typ, false, pkg, "m")
 	if obj == nil {
diff --git a/src/cmd/compile/internal/types2/issues_test.go b/src/cmd/compile/internal/types2/issues_test.go
index 1333870dc98..c7b63a1e680 100644
--- a/src/cmd/compile/internal/types2/issues_test.go
+++ b/src/cmd/compile/internal/types2/issues_test.go
@@ -19,7 +19,7 @@ import (
 )
 
 func TestIssue5770(t *testing.T) {
-	_, err := typecheck("p", `package p; type S struct{T}`, nil)
+	_, err := typecheck("p", `package p; type S struct{T}`, nil, nil)
 	const want = "undefined: T"
 	if err == nil || !strings.Contains(err.Error(), want) {
 		t.Errorf("got: %v; want: %s", err, want)
@@ -39,7 +39,7 @@ var (
 	_ = (interface{})(nil)
 )`
 	types := make(map[syntax.Expr]TypeAndValue)
-	mustTypecheck("p", src, &Info{Types: types})
+	mustTypecheck("p", src, nil, &Info{Types: types})
 
 	for x, tv := range types {
 		var want Type
@@ -78,7 +78,7 @@ func f() int {
 }
 `
 	types := make(map[syntax.Expr]TypeAndValue)
-	mustTypecheck("p", src, &Info{Types: types})
+	mustTypecheck("p", src, nil, &Info{Types: types})
 
 	want := Typ[Int]
 	n := 0
@@ -133,8 +133,6 @@ func _() {
         _, _, _ = x, y, z  // uses x, y, z
 }
 `
-	f := mustParse("", src)
-
 	const want = `L3 defs func p._()
 L4 defs const w untyped int
 L5 defs var x int
@@ -150,8 +148,8 @@ L7 uses var z int`
 	conf := Config{Error: func(err error) { t.Log(err) }}
 	defs := make(map[*syntax.Name]Object)
 	uses := make(map[*syntax.Name]Object)
-	_, err := conf.Check(f.PkgName.Value, []*syntax.File{f}, &Info{Defs: defs, Uses: uses})
-	if s := fmt.Sprint(err); !strings.HasSuffix(s, "cannot assign to w") {
+	_, err := typecheck("p", src, &conf, &Info{Defs: defs, Uses: uses})
+	if s := err.Error(); !strings.HasSuffix(s, "cannot assign to w") {
 		t.Errorf("Check: unexpected error: %s", s)
 	}
 
@@ -230,7 +228,7 @@ func main() {
 `
 	f := func(test, src string) {
 		info := &Info{Uses: make(map[*syntax.Name]Object)}
-		mustTypecheck("main", src, info)
+		mustTypecheck("main", src, nil, info)
 
 		var pkg *Package
 		count := 0
@@ -254,11 +252,11 @@ func main() {
 }
 
 func TestIssue22525(t *testing.T) {
-	f := mustParse("", `package p; func f() { var a, b, c, d, e int }`)
+	const src = `package p; func f() { var a, b, c, d, e int }`
 
 	got := "\n"
 	conf := Config{Error: func(err error) { got += err.Error() + "\n" }}
-	conf.Check(f.PkgName.Value, []*syntax.File{f}, nil) // do not crash
+	typecheck("", src, &conf, nil) // do not crash
 	want := `
 :1:27: a declared and not used
 :1:30: b declared and not used
@@ -443,14 +441,10 @@ func TestIssue34151(t *testing.T) {
 	const asrc = `package a; type I interface{ M() }; type T struct { F interface { I } }`
 	const bsrc = `package b; import "a"; type T struct { F interface { a.I } }; var _ = a.T(T{})`
 
-	a := mustTypecheck("a", asrc, nil)
+	a := mustTypecheck("a", asrc, nil, nil)
 
-	bast := mustParse("", bsrc)
 	conf := Config{Importer: importHelper{pkg: a}}
-	b, err := conf.Check(bast.PkgName.Value, []*syntax.File{bast}, nil)
-	if err != nil {
-		t.Errorf("package %s failed to typecheck: %v", b.Name(), err)
-	}
+	mustTypecheck("b", bsrc, &conf, nil)
 }
 
 type importHelper struct {
@@ -557,13 +551,12 @@ func TestIssue43124(t *testing.T) {
 		csrc = `package c; import ("a"; "html/template"); func _() { a.G(template.Template{}) }`
 	)
 
-	a := mustTypecheck("a", asrc, nil)
+	a := mustTypecheck("a", asrc, nil, nil)
 	conf := Config{Importer: importHelper{pkg: a, fallback: defaultImporter()}}
 
 	// Packages should be fully qualified when there is ambiguity within the
 	// error string itself.
-	bast := mustParse("", bsrc)
-	_, err := conf.Check(bast.PkgName.Value, []*syntax.File{bast}, nil)
+	_, err := typecheck("b", bsrc, &conf, nil)
 	if err == nil {
 		t.Fatal("package b had no errors")
 	}
@@ -572,8 +565,7 @@ func TestIssue43124(t *testing.T) {
 	}
 
 	// ...and also when there is any ambiguity in reachable packages.
-	cast := mustParse("", csrc)
-	_, err = conf.Check(cast.PkgName.Value, []*syntax.File{cast}, nil)
+	_, err = typecheck("c", csrc, &conf, nil)
 	if err == nil {
 		t.Fatal("package c had no errors")
 	}
@@ -671,7 +663,7 @@ func TestIssue51093(t *testing.T) {
 	for _, test := range tests {
 		src := fmt.Sprintf("package p; func _[P %s]() { _ = P(%s) }", test.typ, test.val)
 		types := make(map[syntax.Expr]TypeAndValue)
-		mustTypecheck("p", src, &Info{Types: types})
+		mustTypecheck("p", src, nil, &Info{Types: types})
 
 		var n int
 		for x, tv := range types {
@@ -801,7 +793,7 @@ func (S) M5(struct {S;t}) {}
 
 	test := func(main, b, want string) {
 		re := regexp.MustCompile(want)
-		bpkg := mustTypecheck("b", b, nil)
+		bpkg := mustTypecheck("b", b, nil, nil)
 		mast := mustParse("main.go", main)
 		conf := Config{Importer: importHelper{pkg: bpkg}}
 		_, err := conf.Check(mast.PkgName.Value, []*syntax.File{mast}, nil)
diff --git a/src/cmd/compile/internal/types2/mono_test.go b/src/cmd/compile/internal/types2/mono_test.go
index 506762abae5..17450aa04b1 100644
--- a/src/cmd/compile/internal/types2/mono_test.go
+++ b/src/cmd/compile/internal/types2/mono_test.go
@@ -5,7 +5,6 @@
 package types2_test
 
 import (
-	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/types2"
 	"errors"
 	"fmt"
@@ -15,14 +14,13 @@ import (
 
 func checkMono(t *testing.T, body string) error {
 	src := "package x; import `unsafe`; var _ unsafe.Pointer;\n" + body
-	files := []*syntax.File{mustParse("x.go", src)}
 
 	var buf strings.Builder
 	conf := types2.Config{
 		Error:    func(err error) { fmt.Fprintln(&buf, err) },
 		Importer: defaultImporter(),
 	}
-	conf.Check("x", files, nil)
+	typecheck("x", src, &conf, nil)
 	if buf.Len() == 0 {
 		return nil
 	}
diff --git a/src/cmd/compile/internal/types2/named_test.go b/src/cmd/compile/internal/types2/named_test.go
index 4140bca5397..7938904a932 100644
--- a/src/cmd/compile/internal/types2/named_test.go
+++ b/src/cmd/compile/internal/types2/named_test.go
@@ -31,7 +31,7 @@ func (G[P]) N() (p P) { return }
 
 type Inst = G[int]
 	`
-	pkg := mustTypecheck("p", src, nil)
+	pkg := mustTypecheck("p", src, nil, nil)
 
 	var (
 		T        = pkg.Scope().Lookup("T").Type()
diff --git a/src/cmd/compile/internal/types2/object_test.go b/src/cmd/compile/internal/types2/object_test.go
index 1a0182c8857..ce470034743 100644
--- a/src/cmd/compile/internal/types2/object_test.go
+++ b/src/cmd/compile/internal/types2/object_test.go
@@ -56,7 +56,7 @@ func TestIsAlias(t *testing.T) {
 // the same Func Object as the original method. See also issue #34421.
 func TestEmbeddedMethod(t *testing.T) {
 	const src = `package p; type I interface { error }`
-	pkg := mustTypecheck("p", src, nil)
+	pkg := mustTypecheck("p", src, nil, nil)
 
 	// get original error.Error method
 	eface := Universe.Lookup("error")
@@ -110,7 +110,7 @@ func TestObjectString(t *testing.T) {
 
 	for _, test := range testObjects {
 		src := "package p; " + test.src
-		pkg, err := typecheck(filename, src, nil)
+		pkg, err := typecheck(filename, src, nil, nil)
 		if err != nil {
 			t.Errorf("%s: %s", src, err)
 			continue
diff --git a/src/cmd/compile/internal/types2/sizes_test.go b/src/cmd/compile/internal/types2/sizes_test.go
index e548c2d0478..664eff3cf0d 100644
--- a/src/cmd/compile/internal/types2/sizes_test.go
+++ b/src/cmd/compile/internal/types2/sizes_test.go
@@ -20,7 +20,7 @@ func findStructType(t *testing.T, src string) *types2.Struct {
 
 func findStructTypeConfig(t *testing.T, src string, conf *types2.Config) *types2.Struct {
 	types := make(map[syntax.Expr]types2.TypeAndValue)
-	mustTypecheck("x", src, &types2.Info{Types: types})
+	mustTypecheck("x", src, nil, &types2.Info{Types: types})
 	for _, tv := range types {
 		if ts, ok := tv.Type.(*types2.Struct); ok {
 			return ts
@@ -84,16 +84,12 @@ import "unsafe"
 
 const _ = unsafe.Offsetof(struct{ x int64 }{}.x)
 `
-	f := mustParse("x.go", src)
 	info := types2.Info{Types: make(map[syntax.Expr]types2.TypeAndValue)}
 	conf := types2.Config{
 		Importer: defaultImporter(),
 		Sizes:    &types2.StdSizes{WordSize: 8, MaxAlign: 8},
 	}
-	_, err := conf.Check("x", []*syntax.File{f}, &info)
-	if err != nil {
-		t.Fatal(err)
-	}
+	mustTypecheck("x", src, &conf, &info)
 	for _, tv := range info.Types {
 		_ = conf.Sizes.Sizeof(tv.Type)
 		_ = conf.Sizes.Alignof(tv.Type)
diff --git a/src/cmd/compile/internal/types2/typestring_test.go b/src/cmd/compile/internal/types2/typestring_test.go
index 7dd9b352811..193ee251f09 100644
--- a/src/cmd/compile/internal/types2/typestring_test.go
+++ b/src/cmd/compile/internal/types2/typestring_test.go
@@ -118,7 +118,7 @@ func TestTypeString(t *testing.T) {
 
 	for _, test := range tests {
 		src := `package generic_p; import "io"; type _ io.Writer; type T ` + test.src
-		pkg, err := typecheck(filename, src, nil)
+		pkg, err := typecheck(filename, src, nil, nil)
 		if err != nil {
 			t.Errorf("%s: %s", src, err)
 			continue
@@ -136,8 +136,8 @@ func TestTypeString(t *testing.T) {
 }
 
 func TestQualifiedTypeString(t *testing.T) {
-	p := mustTypecheck("p.go", "package p; type T int", nil)
-	q := mustTypecheck("q.go", "package q", nil)
+	p := mustTypecheck("p.go", "package p; type T int", nil, nil)
+	q := mustTypecheck("q.go", "package q", nil, nil)
 
 	pT := p.Scope().Lookup("T").Type()
 	for _, test := range []struct {
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index ba45ca293ef..b154ad58524 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -36,21 +36,23 @@ func mustParse(fset *token.FileSet, filename, src string) *ast.File {
 	return f
 }
 
-func typecheck(path, src string, info *Info) (*Package, error) {
+func typecheck(path, src string, conf *Config, info *Info) (*Package, error) {
 	fset := token.NewFileSet()
 	f, err := parse(fset, path, src)
 	if f == nil { // ignore errors unless f is nil
 		return nil, err
 	}
-	conf := Config{
-		Error:    func(err error) {}, // collect all errors
-		Importer: importer.Default(),
+	if conf == nil {
+		conf = &Config{
+			Error:    func(err error) {}, // collect all errors
+			Importer: importer.Default(),
+		}
 	}
 	return conf.Check(f.Name.Name, fset, []*ast.File{f}, info)
 }
 
-func mustTypecheck(path, src string, info *Info) *Package {
-	pkg, err := typecheck(path, src, info)
+func mustTypecheck(path, src string, conf *Config, info *Info) *Package {
+	pkg, err := typecheck(path, src, conf, info)
 	if err != nil {
 		panic(err) // so we don't need to pass *testing.T
 	}
@@ -140,7 +142,7 @@ func TestValuesInfo(t *testing.T) {
 		info := Info{
 			Types: make(map[ast.Expr]TypeAndValue),
 		}
-		name := mustTypecheck("ValuesInfo", test.src, &info).Name()
+		name := mustTypecheck("ValuesInfo", test.src, nil, &info).Name()
 
 		// look for expression
 		var expr ast.Expr
@@ -378,7 +380,7 @@ func TestTypesInfo(t *testing.T) {
 		info := Info{Types: make(map[ast.Expr]TypeAndValue)}
 		var name string
 		if strings.HasPrefix(test.src, broken) {
-			pkg, err := typecheck("TypesInfo", test.src, &info)
+			pkg, err := typecheck("TypesInfo", test.src, nil, &info)
 			if err == nil {
 				t.Errorf("package %s: expected to fail but passed", pkg.Name())
 				continue
@@ -387,7 +389,7 @@ func TestTypesInfo(t *testing.T) {
 				name = pkg.Name()
 			}
 		} else {
-			name = mustTypecheck("TypesInfo", test.src, &info).Name()
+			name = mustTypecheck("TypesInfo", test.src, nil, &info).Name()
 		}
 
 		// look for expression type
@@ -552,8 +554,7 @@ type T[P any] []P
 		instMap := make(map[*ast.Ident]Instance)
 		useMap := make(map[*ast.Ident]Object)
 		makePkg := func(src string) *Package {
-			f := mustParse(fset, "p.go", src)
-			pkg, _ := conf.Check("", fset, []*ast.File{f}, &Info{Instances: instMap, Uses: useMap})
+			pkg, _ := typecheck("p.go", src, &conf, &Info{Instances: instMap, Uses: useMap})
 			imports[pkg.Name()] = pkg
 			return pkg
 		}
@@ -648,7 +649,7 @@ func TestDefsInfo(t *testing.T) {
 		info := Info{
 			Defs: make(map[*ast.Ident]Object),
 		}
-		name := mustTypecheck("DefsInfo", test.src, &info).Name()
+		name := mustTypecheck("DefsInfo", test.src, nil, &info).Name()
 
 		// find object
 		var def Object
@@ -715,7 +716,7 @@ func TestUsesInfo(t *testing.T) {
 		info := Info{
 			Uses: make(map[*ast.Ident]Object),
 		}
-		name := mustTypecheck("UsesInfo", test.src, &info).Name()
+		name := mustTypecheck("UsesInfo", test.src, nil, &info).Name()
 
 		// find object
 		var use Object
@@ -856,7 +857,7 @@ func TestImplicitsInfo(t *testing.T) {
 		info := Info{
 			Implicits: make(map[ast.Node]Object),
 		}
-		name := mustTypecheck("ImplicitsInfo", test.src, &info).Name()
+		name := mustTypecheck("ImplicitsInfo", test.src, nil, &info).Name()
 
 		// the test cases expect at most one Implicits entry
 		if len(info.Implicits) > 1 {
@@ -984,7 +985,7 @@ func TestPredicatesInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{Types: make(map[ast.Expr]TypeAndValue)}
-		name := mustTypecheck("PredicatesInfo", test.src, &info).Name()
+		name := mustTypecheck("PredicatesInfo", test.src, nil, &info).Name()
 
 		// look for expression predicates
 		got := "<missing>"
@@ -1076,7 +1077,7 @@ func TestScopesInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{Scopes: make(map[ast.Node]*Scope)}
-		name := mustTypecheck("ScopesInfo", test.src, &info).Name()
+		name := mustTypecheck("ScopesInfo", test.src, nil, &info).Name()
 
 		// number of scopes must match
 		if len(info.Scopes) != len(test.scopes) {
@@ -1264,7 +1265,7 @@ func TestInitOrderInfo(t *testing.T) {
 
 	for _, test := range tests {
 		info := Info{}
-		name := mustTypecheck("InitOrderInfo", test.src, &info).Name()
+		name := mustTypecheck("InitOrderInfo", test.src, nil, &info).Name()
 
 		// number of initializers must match
 		if len(info.InitOrder) != len(test.inits) {
@@ -1354,6 +1355,8 @@ func (m testImporter) Import(path string) (*Package, error) {
 func TestSelection(t *testing.T) {
 	selections := make(map[*ast.SelectorExpr]*Selection)
 
+	// We need a specific fileset in this test below for positions.
+	// Cannot use typecheck helper.
 	fset := token.NewFileSet()
 	imports := make(testImporter)
 	conf := Config{Importer: imports}
@@ -1626,7 +1629,7 @@ func TestLookupFieldOrMethod(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck("test", "package p;"+test.src, nil)
+		pkg := mustTypecheck("test", "package p;"+test.src, nil, nil)
 
 		obj := pkg.Scope().Lookup("a")
 		if obj == nil {
@@ -1905,7 +1908,7 @@ func TestIdentical(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck("test", "package p;"+test.src, nil)
+		pkg := mustTypecheck("test", "package p;"+test.src, nil, nil)
 		X := pkg.Scope().Lookup("X")
 		Y := pkg.Scope().Lookup("Y")
 		if X == nil || Y == nil {
@@ -2184,7 +2187,7 @@ func f(x T) T { return foo.F(x) }
 func TestInstantiate(t *testing.T) {
 	// eventually we like more tests but this is a start
 	const src = "package p; type T[P any] *T[P]"
-	pkg := mustTypecheck(".", src, nil)
+	pkg := mustTypecheck(".", src, nil, nil)
 
 	// type T should have one type parameter
 	T := pkg.Scope().Lookup("T").Type().(*Named)
@@ -2219,7 +2222,7 @@ func TestInstantiateErrors(t *testing.T) {
 
 	for _, test := range tests {
 		src := "package p; " + test.src
-		pkg := mustTypecheck(".", src, nil)
+		pkg := mustTypecheck(".", src, nil, nil)
 
 		T := pkg.Scope().Lookup("T").Type().(*Named)
 
@@ -2542,7 +2545,7 @@ type V4 struct{}
 func (V4) M()
 `
 
-	pkg := mustTypecheck("p.go", src, nil)
+	pkg := mustTypecheck("p.go", src, nil, nil)
 
 	T := pkg.Scope().Lookup("T").Type().Underlying().(*Interface)
 	lookup := func(name string) (*Func, bool) {
diff --git a/src/go/types/builtins_test.go b/src/go/types/builtins_test.go
index 662ececf742..e15bb3242fd 100644
--- a/src/go/types/builtins_test.go
+++ b/src/go/types/builtins_test.go
@@ -7,7 +7,6 @@ package types_test
 import (
 	"fmt"
 	"go/ast"
-	"go/importer"
 	"testing"
 
 	. "go/types"
@@ -174,20 +173,10 @@ func TestBuiltinSignatures(t *testing.T) {
 
 func testBuiltinSignature(t *testing.T, name, src0, want string) {
 	src := fmt.Sprintf(`package p; import "unsafe"; type _ unsafe.Pointer /* use unsafe */; func _[P ~[]byte]() { %s }`, src0)
-	f, err := parse(fset, "", src)
-	if err != nil {
-		t.Errorf("%s: %s", src0, err)
-		return
-	}
 
-	conf := Config{Importer: importer.Default()}
 	uses := make(map[*ast.Ident]Object)
 	types := make(map[ast.Expr]TypeAndValue)
-	_, err = conf.Check(f.Name.Name, fset, []*ast.File{f}, &Info{Uses: uses, Types: types})
-	if err != nil {
-		t.Errorf("%s: %s", src0, err)
-		return
-	}
+	mustTypecheck("p", src, nil, &Info{Uses: uses, Types: types})
 
 	// find called function
 	n := 0
diff --git a/src/go/types/example_test.go b/src/go/types/example_test.go
index 605e9874088..b54a142bd4f 100644
--- a/src/go/types/example_test.go
+++ b/src/go/types/example_test.go
@@ -180,6 +180,8 @@ func fib(x int) int {
 	}
 	return fib(x-1) - fib(x-2)
 }`
+	// We need a specific fileset in this test below for positions.
+	// Cannot use typecheck helper.
 	fset := token.NewFileSet()
 	f := mustParse(fset, "fib.go", input)
 
diff --git a/src/go/types/hilbert_test.go b/src/go/types/hilbert_test.go
index ed7b9866c9a..15e5ae3aca6 100644
--- a/src/go/types/hilbert_test.go
+++ b/src/go/types/hilbert_test.go
@@ -27,7 +27,7 @@ func TestHilbert(t *testing.T) {
 		return
 	}
 
-	mustTypecheck("hilbert.go", string(src), nil)
+	mustTypecheck("hilbert.go", string(src), nil, nil)
 }
 
 func program(n int, out string) []byte {
diff --git a/src/go/types/instantiate_test.go b/src/go/types/instantiate_test.go
index 54e725fc972..91b2a1aaba5 100644
--- a/src/go/types/instantiate_test.go
+++ b/src/go/types/instantiate_test.go
@@ -109,7 +109,7 @@ func TestInstantiateEquality(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		pkg := mustTypecheck(".", test.src, nil)
+		pkg := mustTypecheck(".", test.src, nil, nil)
 
 		t.Run(pkg.Name(), func(t *testing.T) {
 			ctxt := NewContext()
@@ -135,8 +135,8 @@ func TestInstantiateEquality(t *testing.T) {
 
 func TestInstantiateNonEquality(t *testing.T) {
 	const src = "package p; type T[P any] int"
-	pkg1 := mustTypecheck(".", src, nil)
-	pkg2 := mustTypecheck(".", src, nil)
+	pkg1 := mustTypecheck(".", src, nil, nil)
+	pkg2 := mustTypecheck(".", src, nil, nil)
 	// We consider T1 and T2 to be distinct types, so their instances should not
 	// be deduplicated by the context.
 	T1 := pkg1.Scope().Lookup("T").Type().(*Named)
@@ -181,7 +181,7 @@ var X T[int]
 
 	for _, test := range tests {
 		src := prefix + test.decl
-		pkg := mustTypecheck(".", src, nil)
+		pkg := mustTypecheck(".", src, nil, nil)
 		typ := NewPointer(pkg.Scope().Lookup("X").Type())
 		obj, _, _ := LookupFieldOrMethod(typ, false, pkg, "m")
 		m, _ := obj.(*Func)
@@ -203,7 +203,7 @@ func (T[P]) m() {}
 
 var _ T[int]
 `
-	pkg := mustTypecheck(".", src, nil)
+	pkg := mustTypecheck(".", src, nil, nil)
 	typ := pkg.Scope().Lookup("T").Type().(*Named)
 	obj, _, _ := LookupFieldOrMethod(typ, false, pkg, "m")
 	if obj == nil {
diff --git a/src/go/types/issues_test.go b/src/go/types/issues_test.go
index 472faae0ed3..2b7618cbd08 100644
--- a/src/go/types/issues_test.go
+++ b/src/go/types/issues_test.go
@@ -21,7 +21,7 @@ import (
 )
 
 func TestIssue5770(t *testing.T) {
-	_, err := typecheck("p", `package p; type S struct{T}`, nil)
+	_, err := typecheck("p", `package p; type S struct{T}`, nil, nil)
 	const want = "undefined: T"
 	if err == nil || !strings.Contains(err.Error(), want) {
 		t.Errorf("got: %v; want: %s", err, want)
@@ -41,7 +41,7 @@ var (
 	_ = (interface{})(nil)
 )`
 	types := make(map[ast.Expr]TypeAndValue)
-	mustTypecheck("p", src, &Info{Types: types})
+	mustTypecheck("p", src, nil, &Info{Types: types})
 
 	for x, tv := range types {
 		var want Type
@@ -80,7 +80,7 @@ func f() int {
 }
 `
 	types := make(map[ast.Expr]TypeAndValue)
-	mustTypecheck("p", src, &Info{Types: types})
+	mustTypecheck("p", src, nil, &Info{Types: types})
 
 	want := Typ[Int]
 	n := 0
@@ -135,6 +135,9 @@ func _() {
         _, _, _ = x, y, z  // uses x, y, z
 }
 `
+	// We need a specific fileset in this test below for positions.
+	// Cannot use typecheck helper.
+	fset := token.NewFileSet()
 	f := mustParse(fset, "", src)
 
 	const want = `L3 defs func p._()
@@ -153,7 +156,7 @@ L7 uses var z int`
 	defs := make(map[*ast.Ident]Object)
 	uses := make(map[*ast.Ident]Object)
 	_, err := conf.Check(f.Name.Name, fset, []*ast.File{f}, &Info{Defs: defs, Uses: uses})
-	if s := fmt.Sprint(err); !strings.HasSuffix(s, "cannot assign to w") {
+	if s := err.Error(); !strings.HasSuffix(s, "cannot assign to w") {
 		t.Errorf("Check: unexpected error: %s", s)
 	}
 
@@ -232,7 +235,7 @@ func main() {
 `
 	f := func(test, src string) {
 		info := &Info{Uses: make(map[*ast.Ident]Object)}
-		mustTypecheck("main", src, info)
+		mustTypecheck("main", src, nil, info)
 
 		var pkg *Package
 		count := 0
@@ -256,11 +259,11 @@ func main() {
 }
 
 func TestIssue22525(t *testing.T) {
-	f := mustParse(fset, "", `package p; func f() { var a, b, c, d, e int }`)
+	const src = `package p; func f() { var a, b, c, d, e int }`
 
 	got := "\n"
 	conf := Config{Error: func(err error) { got += err.Error() + "\n" }}
-	conf.Check(f.Name.Name, fset, []*ast.File{f}, nil) // do not crash
+	typecheck("", src, &conf, nil) // do not crash
 	want := `
 1:27: a declared and not used
 1:30: b declared and not used
@@ -444,14 +447,10 @@ func TestIssue34151(t *testing.T) {
 	const asrc = `package a; type I interface{ M() }; type T struct { F interface { I } }`
 	const bsrc = `package b; import "a"; type T struct { F interface { a.I } }; var _ = a.T(T{})`
 
-	a := mustTypecheck("a", asrc, nil)
+	a := mustTypecheck("a", asrc, nil, nil)
 
-	bast := mustParse(fset, "", bsrc)
 	conf := Config{Importer: importHelper{pkg: a}}
-	b, err := conf.Check(bast.Name.Name, fset, []*ast.File{bast}, nil)
-	if err != nil {
-		t.Errorf("package %s failed to typecheck: %v", b.Name(), err)
-	}
+	mustTypecheck("b", bsrc, &conf, nil)
 }
 
 type importHelper struct {
@@ -600,7 +599,7 @@ var _ T = template /* ERRORx "cannot use.*text/template.* as T value" */.Templat
 `
 	)
 
-	a := mustTypecheck("a", asrc, nil)
+	a := mustTypecheck("a", asrc, nil, nil)
 	imp := importHelper{pkg: a, fallback: importer.Default()}
 
 	testFiles(t, nil, []string{"b.go"}, [][]byte{[]byte(bsrc)}, false, imp)
@@ -697,7 +696,7 @@ func TestIssue51093(t *testing.T) {
 	for _, test := range tests {
 		src := fmt.Sprintf("package p; func _[P %s]() { _ = P(%s) }", test.typ, test.val)
 		types := make(map[ast.Expr]TypeAndValue)
-		mustTypecheck("p", src, &Info{Types: types})
+		mustTypecheck("p", src, nil, &Info{Types: types})
 
 		var n int
 		for x, tv := range types {
@@ -829,7 +828,7 @@ func (S) M5(struct {S;t}) {}
 	fset := token.NewFileSet()
 	test := func(main, b, want string) {
 		re := regexp.MustCompile(want)
-		bpkg := mustTypecheck("b", b, nil)
+		bpkg := mustTypecheck("b", b, nil, nil)
 		mast := mustParse(fset, "main.go", main)
 		conf := Config{Importer: importHelper{pkg: bpkg}}
 		_, err := conf.Check(mast.Name.Name, fset, []*ast.File{mast}, nil)
diff --git a/src/go/types/methodset_test.go b/src/go/types/methodset_test.go
index 443994be3e6..13ccf9623e3 100644
--- a/src/go/types/methodset_test.go
+++ b/src/go/types/methodset_test.go
@@ -84,7 +84,7 @@ func TestNewMethodSet(t *testing.T) {
 	}
 
 	check := func(src string, methods []method, generic bool) {
-		pkg := mustTypecheck("test", "package p;"+src, nil)
+		pkg := mustTypecheck("test", "package p;"+src, nil, nil)
 
 		scope := pkg.Scope()
 		if generic {
diff --git a/src/go/types/mono_test.go b/src/go/types/mono_test.go
index 9dda2c28f37..a8d2acfd66c 100644
--- a/src/go/types/mono_test.go
+++ b/src/go/types/mono_test.go
@@ -7,25 +7,21 @@ package types_test
 import (
 	"errors"
 	"fmt"
-	"go/ast"
 	"go/importer"
-	"go/token"
 	"go/types"
 	"strings"
 	"testing"
 )
 
 func checkMono(t *testing.T, body string) error {
-	fset := token.NewFileSet()
 	src := "package x; import `unsafe`; var _ unsafe.Pointer;\n" + body
-	files := []*ast.File{mustParse(fset, "x.go", src)}
 
 	var buf strings.Builder
 	conf := types.Config{
 		Error:    func(err error) { fmt.Fprintln(&buf, err) },
 		Importer: importer.Default(),
 	}
-	conf.Check("x", fset, files, nil)
+	typecheck("x", src, &conf, nil)
 	if buf.Len() == 0 {
 		return nil
 	}
diff --git a/src/go/types/named_test.go b/src/go/types/named_test.go
index 92f17e5455e..3cbe1ef83b0 100644
--- a/src/go/types/named_test.go
+++ b/src/go/types/named_test.go
@@ -32,7 +32,7 @@ func (G[P]) N() (p P) { return }
 
 type Inst = G[int]
 	`
-	pkg := mustTypecheck("p", src, nil)
+	pkg := mustTypecheck("p", src, nil, nil)
 
 	var (
 		T        = pkg.Scope().Lookup("T").Type()
diff --git a/src/go/types/object_test.go b/src/go/types/object_test.go
index 5658e38cbe9..912716b9e0b 100644
--- a/src/go/types/object_test.go
+++ b/src/go/types/object_test.go
@@ -58,7 +58,7 @@ func TestIsAlias(t *testing.T) {
 // the same Func Object as the original method. See also issue #34421.
 func TestEmbeddedMethod(t *testing.T) {
 	const src = `package p; type I interface { error }`
-	pkg := mustTypecheck("p", src, nil)
+	pkg := mustTypecheck("p", src, nil, nil)
 
 	// get original error.Error method
 	eface := Universe.Lookup("error")
@@ -112,7 +112,7 @@ func TestObjectString(t *testing.T) {
 
 	for _, test := range testObjects {
 		src := "package p; " + test.src
-		pkg, err := typecheck(filename, src, nil)
+		pkg, err := typecheck(filename, src, nil, nil)
 		if err != nil {
 			t.Errorf("%s: %s", src, err)
 			continue
diff --git a/src/go/types/sizes_test.go b/src/go/types/sizes_test.go
index 09ac9e2c26d..7fbafd82c49 100644
--- a/src/go/types/sizes_test.go
+++ b/src/go/types/sizes_test.go
@@ -9,7 +9,6 @@ package types_test
 import (
 	"go/ast"
 	"go/importer"
-	"go/token"
 	"go/types"
 	"internal/testenv"
 	"testing"
@@ -22,7 +21,7 @@ func findStructType(t *testing.T, src string) *types.Struct {
 
 func findStructTypeConfig(t *testing.T, src string, conf *types.Config) *types.Struct {
 	types_ := make(map[ast.Expr]types.TypeAndValue)
-	mustTypecheck("x", src, &types.Info{Types: types_})
+	mustTypecheck("x", src, nil, &types.Info{Types: types_})
 	for _, tv := range types_ {
 		if ts, ok := tv.Type.(*types.Struct); ok {
 			return ts
@@ -86,17 +85,12 @@ import "unsafe"
 
 const _ = unsafe.Offsetof(struct{ x int64 }{}.x)
 `
-	fset := token.NewFileSet()
-	f := mustParse(fset, "x.go", src)
 	info := types.Info{Types: make(map[ast.Expr]types.TypeAndValue)}
 	conf := types.Config{
 		Importer: importer.Default(),
 		Sizes:    &types.StdSizes{WordSize: 8, MaxAlign: 8},
 	}
-	_, err := conf.Check("x", fset, []*ast.File{f}, &info)
-	if err != nil {
-		t.Fatal(err)
-	}
+	mustTypecheck("x", src, &conf, &info)
 	for _, tv := range info.Types {
 		_ = conf.Sizes.Sizeof(tv.Type)
 		_ = conf.Sizes.Alignof(tv.Type)
diff --git a/src/go/types/typestring_test.go b/src/go/types/typestring_test.go
index e73f24138bd..d3172d6bb9b 100644
--- a/src/go/types/typestring_test.go
+++ b/src/go/types/typestring_test.go
@@ -119,7 +119,7 @@ func TestTypeString(t *testing.T) {
 
 	for _, test := range tests {
 		src := `package p; import "io"; type _ io.Writer; type T ` + test.src
-		pkg, err := typecheck(filename, src, nil)
+		pkg, err := typecheck(filename, src, nil, nil)
 		if err != nil {
 			t.Errorf("%s: %s", src, err)
 			continue
@@ -137,8 +137,8 @@ func TestTypeString(t *testing.T) {
 }
 
 func TestQualifiedTypeString(t *testing.T) {
-	p := mustTypecheck("p.go", "package p; type T int", nil)
-	q := mustTypecheck("q.go", "package q", nil)
+	p := mustTypecheck("p.go", "package p; type T int", nil, nil)
+	q := mustTypecheck("q.go", "package q", nil, nil)
 
 	pT := p.Scope().Lookup("T").Type()
 	for _, test := range []struct {