diff --git a/dependency_updater/dependency_updater.go b/dependency_updater/dependency_updater.go
index 56204d77a..d234d9fd0 100644
--- a/dependency_updater/dependency_updater.go
+++ b/dependency_updater/dependency_updater.go
@@ -407,5 +407,9 @@ func writeToGithubOutput(title string, description string, repoPath string) erro
 }
 
 func generateGithubRepoUrl(dependencies Dependencies, dependencyType string) string {
-	return "https://github.com/" + dependencies[dependencyType].Owner + "/" + dependencies[dependencyType].Repo
+	info := dependencies[dependencyType]
+	if info == nil {
+		return ""
+	}
+	return "https://github.com/" + info.Owner + "/" + info.Repo
 }
diff --git a/dependency_updater/dependency_updater_test.go b/dependency_updater/dependency_updater_test.go
new file mode 100644
index 000000000..e67941a09
--- /dev/null
+++ b/dependency_updater/dependency_updater_test.go
@@ -0,0 +1,389 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestGenerateGithubRepoUrl(t *testing.T) {
+	deps := Dependencies{
+		"op_node":     {Owner: "ethereum-optimism", Repo: "optimism"},
+		"base_reth":   {Owner: "base", Repo: "base"},
+		"nethermind":  {Owner: "NethermindEth", Repo: "nethermind"},
+		"op_geth":     {Owner: "ethereum-optimism", Repo: "op-geth"},
+	}
+
+	tests := []struct {
+		name     string
+		depType  string
+		expected string
+	}{
+		{"op_node", "op_node", "https://github.com/ethereum-optimism/optimism"},
+		{"base_reth", "base_reth", "https://github.com/base/base"},
+		{"nethermind", "nethermind", "https://github.com/NethermindEth/nethermind"},
+		{"op_geth", "op_geth", "https://github.com/ethereum-optimism/op-geth"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := generateGithubRepoUrl(deps, tt.depType)
+			if got != tt.expected {
+				t.Errorf("generateGithubRepoUrl() = %q, want %q", got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestGenerateGithubRepoUrl_UnknownDependency(t *testing.T) {
+	deps := Dependencies{
+		"known": {Owner: "test", Repo: "repo"},
+	}
+
+	// Accessing an unknown key returns nil, which should return empty string
+	result := generateGithubRepoUrl(deps, "unknown")
+	expected := ""
+	if result != expected {
+		t.Errorf("generateGithubRepoUrl() for unknown key = %q, want %q", result, expected)
+	}
+}
+
+func TestWriteToVersionsJson(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	deps := Dependencies{
+		"test_dep": {
+			Tag:    "v1.0.0",
+			Commit: "abc123def456",
+			Owner:  "testowner",
+			Repo:   "testrepo",
+		},
+	}
+
+	err := writeToVersionsJson(tmpDir, deps)
+	if err != nil {
+		t.Fatalf("writeToVersionsJson() returned error: %v", err)
+	}
+
+	// Verify the file was created
+	data, err := os.ReadFile(filepath.Join(tmpDir, "versions.json"))
+	if err != nil {
+		t.Fatalf("failed to read versions.json: %v", err)
+	}
+
+	content := string(data)
+	if !strings.Contains(content, `"tag": "v1.0.0"`) {
+		t.Errorf("versions.json missing tag: %s", content)
+	}
+	if !strings.Contains(content, `"commit": "abc123def456"`) {
+		t.Errorf("versions.json missing commit: %s", content)
+	}
+	if !strings.Contains(content, `"owner": "testowner"`) {
+		t.Errorf("versions.json missing owner: %s", content)
+	}
+}
+
+func TestWriteToVersionsJson_InvalidPath(t *testing.T) {
+	deps := Dependencies{
+		"test": {Tag: "v1.0.0", Commit: "abc", Owner: "o", Repo: "r"},
+	}
+
+	err := writeToVersionsJson("/nonexistent/path", deps)
+	if err == nil {
+		t.Error("writeToVersionsJson() expected error for invalid path, got nil")
+	}
+}
+
+func TestCreateVersionsEnv_Basic(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	deps := Dependencies{
+		"base_reth_node": {
+			Tag:    "v0.8.0",
+			Commit: "3049ce2e3a5132f2ef74b4ba14a1a952ea6abdfb",
+			Owner:  "base",
+			Repo:   "base",
+		},
+		"op_node": {
+			Tag:    "op-node/v1.16.11",
+			Commit: "cba7aba0c98aae22720b21c3a023990a486cb6e0",
+			Owner:  "ethereum-optimism",
+			Repo:   "optimism",
+		},
+	}
+
+	err := createVersionsEnv(tmpDir, deps)
+	if err != nil {
+		t.Fatalf("createVersionsEnv() returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(tmpDir, "versions.env"))
+	if err != nil {
+		t.Fatalf("failed to read versions.env: %v", err)
+	}
+
+	content := string(data)
+
+	// Verify all expected variables exist
+	checks := []string{
+		"export BASE_RETH_NODE_TAG=v0.8.0",
+		"export BASE_RETH_NODE_COMMIT=3049ce2e3a5132f2ef74b4ba14a1a952ea6abdfb",
+		"export BASE_RETH_NODE_REPO=https://github.com/base/base.git",
+		"export OP_NODE_TAG=op-node/v1.16.11",
+		"export OP_NODE_COMMIT=cba7aba0c98aae22720b21c3a023990a486cb6e0",
+		"export OP_NODE_REPO=https://github.com/ethereum-optimism/optimism.git",
+	}
+
+	for _, check := range checks {
+		if !strings.Contains(content, check) {
+			t.Errorf("versions.env missing expected line: %q", check)
+		}
+	}
+}
+
+func TestCreateVersionsEnv_BranchTracking(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	deps := Dependencies{
+		"tracking_branch": {
+			Tag:      "", // Tag should be empty for branch tracking
+			Commit:   "oldcommit123",
+			Owner:    "test",
+			Repo:     "test",
+			Branch:   "main",
+			Tracking: "branch",
+		},
+	}
+
+	err := createVersionsEnv(tmpDir, deps)
+	if err != nil {
+		t.Fatalf("createVersionsEnv() returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(tmpDir, "versions.env"))
+	if err != nil {
+		t.Fatalf("failed to read versions.env: %v", err)
+	}
+
+	content := string(data)
+
+	// For branch tracking, Tag should be replaced with Branch name
+	if !strings.Contains(content, "export TRACKING_BRANCH_TAG=main") {
+		t.Errorf("branch tracking: expected TAG=main, got: %s", content)
+	}
+	if !strings.Contains(content, "export TRACKING_BRANCH_COMMIT=oldcommit123") {
+		t.Errorf("branch tracking: expected COMMIT=oldcommit123, got: %s", content)
+	}
+}
+
+func TestCreateVersionsEnv_SortedOutput(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	deps := Dependencies{
+		"zeta": {Tag: "v1.0.0", Commit: "a", Owner: "o", Repo: "r"},
+		"alpha": {Tag: "v1.0.0", Commit: "b", Owner: "o", Repo: "r"},
+		"beta":  {Tag: "v1.0.0", Commit: "c", Owner: "o", Repo: "r"},
+	}
+
+	err := createVersionsEnv(tmpDir, deps)
+	if err != nil {
+		t.Fatalf("createVersionsEnv() returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(tmpDir, "versions.env"))
+	if err != nil {
+		t.Fatalf("failed to read versions.env: %v", err)
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(data)), "\n")
+
+	// Verify alphabetical ordering: ALPHA, BETA, ZETA
+	if len(lines) < 3 {
+		t.Fatalf("expected at least 3 lines, got %d", len(lines))
+	}
+
+	// Check lines are sorted — first line should start with ALPHA, last with ZETA
+	if !strings.HasPrefix(lines[0], "export ALPHA_") {
+		t.Errorf("expected first line to start with ALPHA_, got: %s", lines[0])
+	}
+	if !strings.HasPrefix(lines[len(lines)-1], "export ZETA_") {
+		t.Errorf("expected last line to start with ZETA_, got: %s", lines[len(lines)-1])
+	}
+}
+
+func TestCreateVersionsEnv_InvalidPath(t *testing.T) {
+	deps := Dependencies{
+		"test": {Tag: "v1.0.0", Commit: "abc", Owner: "o", Repo: "r"},
+	}
+
+	err := createVersionsEnv("/nonexistent/path", deps)
+	if err == nil {
+		t.Error("createVersionsEnv() expected error for invalid path, got nil")
+	}
+}
+
+func TestWriteToGithubOutput(t *testing.T) {
+	tmpDir := t.TempDir()
+	outputFile := filepath.Join(tmpDir, "github_output.txt")
+
+	// Set GITHUB_OUTPUT env var for the test
+	t.Setenv("GITHUB_OUTPUT", outputFile)
+
+	title := "chore: updated repo1, repo2"
+	description := "### Dependency Updates\n**repo1** - v1.0.0: [diff](url1)\n**repo2** - v2.0.0: [diff](url2)"
+
+	err := writeToGithubOutput(title, description, tmpDir)
+	if err != nil {
+		t.Fatalf("writeToGithubOutput() returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(outputFile)
+	if err != nil {
+		t.Fatalf("failed to read GITHUB_OUTPUT: %v", err)
+	}
+
+	content := string(data)
+
+	if !strings.Contains(content, "TITLE=chore: updated repo1, repo2") {
+		t.Errorf("GITHUB_OUTPUT missing TITLE, got: %s", content)
+	}
+	if !strings.Contains(content, "DESC<<EOF") {
+		t.Errorf("GITHUB_OUTPUT missing DESC delimiter, got: %s", content)
+	}
+	if !strings.Contains(content, "repo1") || !strings.Contains(content, "repo2") {
+		t.Errorf("GITHUB_OUTPUT missing repo descriptions, got: %s", content)
+	}
+	if !strings.Contains(content, "EOF") {
+		t.Errorf("GITHUB_OUTPUT missing closing EOF, got: %s", content)
+	}
+}
+
+func TestWriteToGithubOutput_NoEnvVar(t *testing.T) {
+	// Unset GITHUB_OUTPUT if it was set
+	if prev, ok := os.LookupEnv("GITHUB_OUTPUT"); ok {
+		defer os.Setenv("GITHUB_OUTPUT", prev)
+		os.Unsetenv("GITHUB_OUTPUT")
+	}
+
+	err := writeToGithubOutput("title", "desc", "/tmp")
+	if err == nil {
+		t.Error("writeToGithubOutput() expected error when GITHUB_OUTPUT is unset, got nil")
+	}
+}
+
+func TestCreateCommitMessage_NeedsGitRepo(t *testing.T) {
+	// createCommitMessage runs `git commit` so it requires a real git repo.
+	// We verify the githubAction=true path works instead.
+	t.Skip("Skipping: createCommitMessage local mode requires a git repository")
+}
+
+func TestCreateCommitMessage_GithubActionMode(t *testing.T) {
+	tmpDir := t.TempDir()
+	outputFile := filepath.Join(tmpDir, "github_output.txt")
+	t.Setenv("GITHUB_OUTPUT", outputFile)
+
+	updates := []VersionUpdateInfo{
+		{
+			Repo:    "base/base",
+			From:    "v0.7.0",
+			To:      "v0.8.0",
+			DiffUrl: "https://github.com/base/base/compare/v0.7.0...v0.8.0",
+		},
+		{
+			Repo:    "ethereum-optimism/op-geth",
+			From:    "v1.101701.0",
+			To:      "v1.101702.0",
+			DiffUrl: "https://github.com/ethereum-optimism/op-geth/compare/v1.101701.0...v1.101702.0",
+		},
+	}
+
+	err := createCommitMessage(updates, tmpDir, true)
+	if err != nil {
+		t.Fatalf("createCommitMessage(githubAction=true) returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(outputFile)
+	if err != nil {
+		t.Fatalf("failed to read GITHUB_OUTPUT: %v", err)
+	}
+
+	content := string(data)
+
+	// Verify the title contains both repos
+	if !strings.Contains(content, "base/base") {
+		t.Errorf("commit title missing base/base, got: %s", content)
+	}
+	if !strings.Contains(content, "ethereum-optimism/op-geth") {
+		t.Errorf("commit title missing op-geth, got: %s", content)
+	}
+
+	// Verify description has the dependency update section
+	if !strings.Contains(content, "### Dependency Updates") {
+		t.Errorf("commit description missing header")
+	}
+}
+
+func TestUpdateVersionTagAndCommit(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	deps := Dependencies{
+		"test_dep": {
+			Tag:    "v1.0.0",
+			Commit: "oldcommit",
+			Owner:  "test",
+			Repo:   "test",
+		},
+	}
+
+	// Update to new version
+	err := updateVersionTagAndCommit("newcommit456", "v2.0.0", "test_dep", tmpDir, deps)
+	if err != nil {
+		t.Fatalf("updateVersionTagAndCommit() returned error: %v", err)
+	}
+
+	// Verify in-memory update
+	if deps["test_dep"].Tag != "v2.0.0" {
+		t.Errorf("expected Tag=v2.0.0, got %q", deps["test_dep"].Tag)
+	}
+	if deps["test_dep"].Commit != "newcommit456" {
+		t.Errorf("expected Commit=newcommit456, got %q", deps["test_dep"].Commit)
+	}
+
+	// Verify file write
+	data, err := os.ReadFile(filepath.Join(tmpDir, "versions.json"))
+	if err != nil {
+		t.Fatalf("failed to read versions.json: %v", err)
+	}
+	content := string(data)
+	if !strings.Contains(content, `"tag": "v2.0.0"`) {
+		t.Errorf("versions.json not updated on disk: %s", content)
+	}
+}
+
+func TestNoUpdatesDoesNotCreateCommit(t *testing.T) {
+	// When updatedDependencies is nil/empty, commit should not be created
+	// This tests the condition in updater(): `if (commit && updatedDependencies != nil)`
+
+	tmpDir := t.TempDir()
+	outputFile := filepath.Join(tmpDir, "github_output.txt")
+	t.Setenv("GITHUB_OUTPUT", outputFile)
+
+	// Empty updates slice — should not write anything
+	err := createCommitMessage([]VersionUpdateInfo{}, tmpDir, true)
+	if err != nil {
+		t.Fatalf("createCommitMessage empty updates returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(outputFile)
+	if err != nil {
+		t.Fatalf("failed to read GITHUB_OUTPUT: %v", err)
+	}
+
+	content := string(data)
+	// The function should write even with empty updates since cmd is still called
+	// But the title should just be "chore: updated " with no repos
+	if !strings.Contains(content, "TITLE=chore: updated") {
+		t.Errorf("expected basic title, got: %s", content)
+	}
+}