diff --git a/bake/hcl_test.go b/bake/hcl_test.go
index c18c5286..1881543b 100644
--- a/bake/hcl_test.go
+++ b/bake/hcl_test.go
@@ -8,65 +8,156 @@ import (
 )
 
 func TestParseHCL(t *testing.T) {
-	os.Setenv("BUILD_NUMBER", "456")
-
-	var dt = []byte(`
-	variable "BUILD_NUMBER" {
-		default = "123"
-	}
-
-	group "default" {
-		targets = ["db", "webapp"]
-	}
-
-	target "db" {
-		context = "./db"
-		tags = ["docker.io/tonistiigi/db"]
-	}
-
-	target "webapp" {
-		context = "./dir"
-		dockerfile = "Dockerfile-alternate"
-		args = {
-			buildno = "${BUILD_NUMBER}"
+	t.Parallel()
+
+	t.Run("Basic", func(t *testing.T) {
+		dt := []byte(`
+		group "default" {
+			targets = ["db", "webapp"]
+		}
+
+		target "db" {
+			context = "./db"
+			tags = ["docker.io/tonistiigi/db"]
+		}
+
+		target "webapp" {
+			context = "./dir"
+			dockerfile = "Dockerfile-alternate"
+			args = {
+				buildno = "123"
+			}
 		}
-	}
-
-	target "cross" {
-		platforms = [
-			"linux/amd64",
-			"linux/arm64"
-		]
-	}
-
-	target "webapp-plus" {
-		inherits = ["webapp", "cross"]
-		args = {
-			IAMCROSS = "true"
+
+		target "cross" {
+			platforms = [
+				"linux/amd64",
+				"linux/arm64"
+			]
+		}
+
+		target "webapp-plus" {
+			inherits = ["webapp", "cross"]
+			args = {
+				IAMCROSS = "true"
+			}
 		}
-	}
-	`)
+		`)
+
+		c, err := ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Groups))
+		require.Equal(t, "default", c.Groups[0].Name)
+		require.Equal(t, []string{"db", "webapp"}, c.Groups[0].Targets)
 
-	c, err := ParseHCL(dt, "docker-bake.hcl")
-	require.NoError(t, err)
+		require.Equal(t, 4, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "db")
+		require.Equal(t, "./db", *c.Targets[0].Context)
 
-	require.Equal(t, 1, len(c.Groups))
-	require.Equal(t, "default", c.Groups[0].Name)
-	require.Equal(t, []string{"db", "webapp"}, c.Groups[0].Targets)
+		require.Equal(t, c.Targets[1].Name, "webapp")
+		require.Equal(t, 1, len(c.Targets[1].Args))
+		require.Equal(t, "123", c.Targets[1].Args["buildno"])
 
-	require.Equal(t, 4, len(c.Targets))
-	require.Equal(t, c.Targets[0].Name, "db")
-	require.Equal(t, "./db", *c.Targets[0].Context)
+		require.Equal(t, c.Targets[2].Name, "cross")
+		require.Equal(t, 2, len(c.Targets[2].Platforms))
+		require.Equal(t, []string{"linux/amd64", "linux/arm64"}, c.Targets[2].Platforms)
 
-	require.Equal(t, c.Targets[1].Name, "webapp")
-	require.Equal(t, 1, len(c.Targets[1].Args))
-	require.Equal(t, "456", c.Targets[1].Args["buildno"])
+		require.Equal(t, c.Targets[3].Name, "webapp-plus")
+		require.Equal(t, 1, len(c.Targets[3].Args))
+		require.Equal(t, map[string]string{"IAMCROSS": "true"}, c.Targets[3].Args)
+	})
+
+	t.Run("WithFunctions", func(t *testing.T) {
+		dt := []byte(`
+		group "default" {
+			targets = ["webapp"]
+		}
+
+		target "webapp" {
+			args = {
+				buildno = "${add(123, 1)}"
+			}
+		}
+		`)
+
+		c, err := ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Groups))
+		require.Equal(t, "default", c.Groups[0].Name)
+		require.Equal(t, []string{"webapp"}, c.Groups[0].Targets)
+
+		require.Equal(t, 1, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "webapp")
+		require.Equal(t, "124", c.Targets[0].Args["buildno"])
+	})
+
+	t.Run("WithVariables", func(t *testing.T) {
+		dt := []byte(`
+		variable "BUILD_NUMBER" {
+			default = "123"
+		}
 
-	require.Equal(t, c.Targets[2].Name, "cross")
-	require.Equal(t, 2, len(c.Targets[2].Platforms))
-	require.Equal(t, []string{"linux/amd64", "linux/arm64"}, c.Targets[2].Platforms)
+		group "default" {
+			targets = ["webapp"]
+		}
+
+		target "webapp" {
+			args = {
+				buildno = "${BUILD_NUMBER}"
+			}
+		}
+		`)
+
+		c, err := ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Groups))
+		require.Equal(t, "default", c.Groups[0].Name)
+		require.Equal(t, []string{"webapp"}, c.Groups[0].Targets)
+
+		require.Equal(t, 1, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "webapp")
+		require.Equal(t, "123", c.Targets[0].Args["buildno"])
+
+		os.Setenv("BUILD_NUMBER", "456")
+
+		c, err = ParseHCL(dt, "docker-bake.hcl")
+		require.NoError(t, err)
+
+		require.Equal(t, 1, len(c.Groups))
+		require.Equal(t, "default", c.Groups[0].Name)
+		require.Equal(t, []string{"webapp"}, c.Groups[0].Targets)
+
+		require.Equal(t, 1, len(c.Targets))
+		require.Equal(t, c.Targets[0].Name, "webapp")
+		require.Equal(t, "456", c.Targets[0].Args["buildno"])
+	})
+
+	t.Run("WithIncorrectVariables", func(t *testing.T) {
+		dt := []byte(`
+		variable "DEFAULT_BUILD_NUMBER" {
+			default = "1"
+		}
+
+		variable "BUILD_NUMBER" {
+			default = "${DEFAULT_BUILD_NUMBER}"
+		}
+
+		group "default" {
+			targets = ["webapp"]
+		}
+
+		target "webapp" {
+			args = {
+				buildno = "${BUILD_NUMBER}"
+			}
+		}
+		`)
 
-	require.Equal(t, c.Targets[3].Name, "webapp-plus")
-	require.Equal(t, 1, len(c.Targets[3].Args))
-	require.Equal(t, map[string]string{"IAMCROSS": "true"}, c.Targets[3].Args)
+		_, err := ParseHCL(dt, "docker-bake.hcl")
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "docker-bake.hcl:7,17-37: Variables not allowed; Variables may not be used here.")
+	})
 }