diff --git a/pkg/workflow/errors.go b/pkg/workflow/errors.go
new file mode 100644
index 0000000..7899e86
--- /dev/null
+++ b/pkg/workflow/errors.go
@@ -0,0 +1,10 @@
+package workflow
+
+import (
+	"errors"
+)
+
+var (
+	ErrNoNodesFound      = errors.New("no nodes found in the graph")
+	ErrEntryNodeNotFound = errors.New("\"entry\" node not found")
+)
diff --git a/pkg/workflow/graph.go b/pkg/workflow/graph.go
index ba6d74a..983fb05 100644
--- a/pkg/workflow/graph.go
+++ b/pkg/workflow/graph.go
@@ -3,7 +3,6 @@ package workflow
 import (
 	"bytes"
 	"encoding/base64"
-	"fmt"
 
 	v1alpha13 "github.com/argoproj/argo-workflows/v3/pkg/apis/workflow/v1alpha1"
 	fluxhelmv2beta1 "github.com/fluxcd/helm-controller/api/v2beta1"
@@ -22,8 +21,8 @@ type Node struct {
 }
 
 func Build(entry string, nodes map[string]v1alpha13.NodeStatus) (*Graph, error) {
-	if nodes == nil || len(nodes) == 0 {
-		return nil, fmt.Errorf("no nodes found in the graph")
+	if len(nodes) == 0 {
+		return nil, ErrNoNodesFound
 	}
 
 	g := &Graph{
@@ -33,7 +32,7 @@ func Build(entry string, nodes map[string]v1alpha13.NodeStatus) (*Graph, error)
 
 	e, ok := nodes[entry]
 	if !ok {
-		return nil, fmt.Errorf("\"entry\" node not found")
+		return nil, ErrEntryNodeNotFound
 	}
 
 	err := g.bft(e)
diff --git a/pkg/workflow/graph_test.go b/pkg/workflow/graph_test.go
new file mode 100644
index 0000000..8079a69
--- /dev/null
+++ b/pkg/workflow/graph_test.go
@@ -0,0 +1,56 @@
+package workflow
+
+import (
+	"testing"
+
+	v1alpha13 "github.com/argoproj/argo-workflows/v3/pkg/apis/workflow/v1alpha1"
+)
+
+func TestBuild(t *testing.T) {
+	type args struct {
+		entry string
+		nodes map[string]v1alpha13.NodeStatus
+	}
+	testmap := make(map[string]v1alpha13.NodeStatus)
+	testmap["dummy"] = v1alpha13.NodeStatus{}
+
+	tests := []struct {
+		name string
+		args args
+		want *Graph
+		err  error
+	}{
+		//
+		// TODO: Add more test cases.
+		//
+		{
+			name: "testing nil nodes",
+			args: args{
+				entry: "",
+				nodes: nil,
+			},
+			want: nil,
+			err:  ErrNoNodesFound,
+		},
+		{
+			name: "testing unknown entry",
+			args: args{
+				entry: "unknown",
+				nodes: testmap,
+			},
+			want: nil,
+			err:  ErrEntryNodeNotFound,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Build(tt.args.entry, tt.args.nodes)
+			if err != tt.err {
+				t.Errorf("Build() error = %v, want %v", err, tt.err)
+			}
+			if got != tt.want {
+				t.Errorf("Build() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}