diff --git a/.github/workflows/packages.yml b/.github/workflows/packages.yml
index e471ee7..8cfbe4b 100644
--- a/.github/workflows/packages.yml
+++ b/.github/workflows/packages.yml
@@ -930,7 +930,7 @@ jobs:
       - name: Test
         working-directory: md4
         run: go test ./...
-  golang-go:
+  golang-go-src-crypto-internal-bigmod:
     runs-on: ubuntu-latest
     steps:
       - name: Install Go
@@ -947,7 +947,45 @@ jobs:
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
         with:
           repository: golang/go
-          ref: go1.19
+          ref: go1.20rc2
+          path: go
+          persist-credentials: false
+      - name: Compile Go Toolchain
+        working-directory: go/src
+        run: ./make.bash
+      - name: Avo Module Replacement
+        working-directory: go/src/crypto/internal/bigmod/_asm
+        run: |
+          go mod edit -modfile=go.mod -require=github.com/mmcloughlin/avo@v0.0.0-00010101000000-000000000000
+          go mod edit -modfile=go.mod -replace=github.com/mmcloughlin/avo=${{ github.workspace }}/avo
+          go mod tidy -modfile=go.mod
+      - name: Generate
+        working-directory: go
+        run: env --unset=GOROOT ./bin/go generate -v -x ./src/crypto/internal/bigmod/_asm
+      - name: Diff
+        working-directory: go
+        run: git diff
+      - name: Test
+        working-directory: go
+        run: env --unset=GOROOT ./bin/go test crypto/...
+  golang-go-src-crypto-internal-edwards25519:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
+        with:
+          go-version: 1.19.x
+          check-latest: true
+      - name: Checkout avo
+        uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
+        with:
+          path: avo
+          persist-credentials: false
+      - name: Checkout golang/go
+        uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0
+        with:
+          repository: golang/go
+          ref: go1.20rc2
           path: go
           persist-credentials: false
       - name: Compile Go Toolchain
@@ -960,8 +998,8 @@ jobs:
           go mod edit -modfile=go.mod -replace=github.com/mmcloughlin/avo=${{ github.workspace }}/avo
           go mod tidy -modfile=go.mod
       - name: Generate
-        working-directory: go/src/crypto/internal/edwards25519/field/_asm
-        run: go generate -v -x
+        working-directory: go
+        run: env --unset=GOROOT ./bin/go generate -v -x ./src/crypto/internal/edwards25519/field/_asm
       - name: Diff
         working-directory: go
         run: git diff
diff --git a/.github/workflows/thirdparty.yml b/.github/workflows/thirdparty.yml
index bb09359..2b11a12 100644
--- a/.github/workflows/thirdparty.yml
+++ b/.github/workflows/thirdparty.yml
@@ -25,4 +25,4 @@ jobs:
           persist-credentials: false
       - name: Run Third-Party Tests
         working-directory: tests/thirdparty
-        run: go test -net -suite suite.json
+        run: go test -timeout 15m -args -net -suite suite.json
diff --git a/tests/thirdparty/config.go b/tests/thirdparty/config.go
index 2634623..5c16be2 100644
--- a/tests/thirdparty/config.go
+++ b/tests/thirdparty/config.go
@@ -132,9 +132,8 @@ func (s *Step) Validate() error {
 
 // Package defines an integration test for a package within a project.
 type Package struct {
-	// Sub-package within the project under test. All file path references will
-	// be relative to this directory. If empty the root of the repository is
-	// used.
+	// Sub-package within the project under test. Used as the root directory for
+	// the test unless explicitly overridden.
 	SubPackage string `json:"pkg,omitempty"`
 
 	// Path to the module file for the avo generator package. This is necessary
@@ -142,6 +141,11 @@ type Package struct {
 	// version under test.
 	Module string `json:"module"`
 
+	// Root directory for all steps in the test. All file path references will
+	// be relative to this directory. If empty, the sub-package directory is
+	// used, or otherwise the root of the repository.
+	Root string `json:"root,omitempty"`
+
 	// Setup steps. These run prior to the insertion of avo replace directives,
 	// therefore should be used if it's necessary to initialize new go modules
 	// within the repository.
@@ -219,6 +223,17 @@ func (p *Package) IsRoot() bool {
 	return p.SubPackage == ""
 }
 
+// WorkingDirectory returns the base directory for all steps in the test.
+func (p *Package) WorkingDirectory() string {
+	if p.Root != "" {
+		return p.Root
+	}
+	if p.SubPackage != "" {
+		return p.SubPackage
+	}
+	return ""
+}
+
 // Context specifies execution environment parameters for a third-party test.
 type Context struct {
 	// Path to the avo version under test.
@@ -272,9 +287,9 @@ func (p *Package) Steps(c *Context) []*Step {
 	}
 
 	// Prepend sub-directory to every step.
-	if p.SubPackage != "" {
+	if dir := p.WorkingDirectory(); dir != "" {
 		for _, s := range steps {
-			s.WorkingDirectory = filepath.Join(p.SubPackage, s.WorkingDirectory)
+			s.WorkingDirectory = filepath.Join(dir, s.WorkingDirectory)
 		}
 	}
 
@@ -304,20 +319,33 @@ func (p Projects) defaults(set bool) {
 
 // Validate the project collection.
 func (p Projects) Validate() error {
-	seen := map[string]bool{}
+	// Projects are valid.
 	for _, prj := range p {
-		// Project is valid.
 		if err := prj.Validate(); err != nil {
 			return fmt.Errorf("project %s: %w", prj.ID(), err)
 		}
+	}
 
-		// No duplicate entries.
+	// No duplicate project IDs.
+	pid := map[string]bool{}
+	for _, prj := range p {
 		id := prj.ID()
-		if seen[id] {
+		if pid[id] {
 			return fmt.Errorf("duplicate project %q", id)
 		}
-		seen[id] = true
+		pid[id] = true
 	}
+
+	// No duplicate test IDs.
+	tid := map[string]bool{}
+	for _, t := range p.Tests() {
+		id := t.ID()
+		if tid[id] {
+			return fmt.Errorf("duplicate test %q", id)
+		}
+		tid[id] = true
+	}
+
 	return nil
 }
 
diff --git a/tests/thirdparty/packages_test.go b/tests/thirdparty/packages_test.go
index fa5a7d6..d34b9ce 100644
--- a/tests/thirdparty/packages_test.go
+++ b/tests/thirdparty/packages_test.go
@@ -2,6 +2,7 @@ package thirdparty
 
 import (
 	"flag"
+	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
@@ -69,6 +70,7 @@ type PackageTest struct {
 // Run the test.
 func (t *PackageTest) Run() {
 	t.checkout()
+	t.validate()
 	t.steps()
 }
 
@@ -88,6 +90,24 @@ func (t *PackageTest) checkout() {
 	test.Exec(t.T, "git", "-C", t.repopath, "checkout", "FETCH_HEAD")
 }
 
+// validate the test configuration relative to the checked out project.
+func (t *PackageTest) validate() {
+	// Confirm expected directories exist.
+	expect := map[string]string{
+		"package": t.Package.SubPackage,
+		"root":    t.Package.WorkingDirectory(),
+	}
+	for name, subdir := range expect {
+		if subdir == "" {
+			continue
+		}
+		path := filepath.Join(t.repopath, subdir)
+		if _, err := os.Stat(path); err != nil {
+			t.Fatalf("expected %s directory: %s", name, err)
+		}
+	}
+}
+
 func (t *PackageTest) steps() {
 	// Determine the path to avo.
 	_, self, _, ok := runtime.Caller(1)
diff --git a/tests/thirdparty/suite.json b/tests/thirdparty/suite.json
index d9ac6b6..1901ea9 100644
--- a/tests/thirdparty/suite.json
+++ b/tests/thirdparty/suite.json
@@ -749,9 +749,39 @@
                 "stars": 107376
             },
             "default_branch": "master",
-            "version": "go1.19",
+            "version": "go1.20rc2",
             "packages": [
                 {
+                    "pkg": "src/crypto/internal/bigmod",
+                    "root": ".",
+                    "module": "src/crypto/internal/bigmod/_asm/go.mod",
+                    "setup": [
+                        {
+                            "name": "Compile Go Toolchain",
+                            "dir": "src",
+                            "commands": [
+                                "./make.bash"
+                            ]
+                        }
+                    ],
+                    "generate": [
+                        {
+                            "commands": [
+                                "env --unset=GOROOT ./bin/go generate -v -x ./src/crypto/internal/bigmod/_asm"
+                            ]
+                        }
+                    ],
+                    "test": [
+                        {
+                            "commands": [
+                                "env --unset=GOROOT ./bin/go test crypto/..."
+                            ]
+                        }
+                    ]
+                },
+                {
+                    "pkg": "src/crypto/internal/edwards25519",
+                    "root": ".",
                     "module": "src/crypto/internal/edwards25519/field/_asm/go.mod",
                     "setup": [
                         {
@@ -764,9 +794,8 @@
                     ],
                     "generate": [
                         {
-                            "dir": "src/crypto/internal/edwards25519/field/_asm",
                             "commands": [
-                                "go generate -v -x"
+                                "env --unset=GOROOT ./bin/go generate -v -x ./src/crypto/internal/edwards25519/field/_asm"
                             ]
                         }
                     ],