diff --git a/internal/osbuild/assembler_test.go b/internal/osbuild/assembler_test.go
new file mode 100644
index 000000000..ffef02565
--- /dev/null
+++ b/internal/osbuild/assembler_test.go
@@ -0,0 +1,159 @@
+package osbuild
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAssembler_UnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name          string
+		assembler     Assembler
+		data          []byte
+		errorExpected bool
+	}{
+		{
+			// invalid JSON - note the missing brace at the end of the string
+			name:          "invalid json",
+			data:          []byte(`{"name":"org.osbuild.tar","options":{"filename":"",size:0}`),
+			errorExpected: true,
+		},
+		{
+			// valid JSON, but with an unknown assembler (org.osbuild.foo)
+			name:          "unknown assembler",
+			data:          []byte(`{"name":"org.osbuild.foo","options":{"bar":null}}`),
+			errorExpected: true,
+		},
+		{
+			name:          "missing options",
+			data:          []byte(`{"name":"org.osbuild.rawfs"`),
+			errorExpected: true,
+		},
+		{
+			name:          "missing name",
+			data:          []byte(`{"options":{"bar":null}}`),
+			errorExpected: true,
+		},
+		{
+			name: "qemu assembler empty",
+			assembler: Assembler{
+				Name:    "org.osbuild.qemu",
+				Options: &QEMUAssemblerOptions{},
+			},
+			data: []byte(`{"name":"org.osbuild.qemu","options":{"format":"","filename":"","size":0,"ptuuid":"","pttype":"","partitions":null}}`),
+		},
+		{
+			name: "qemu assembler full",
+			assembler: Assembler{
+				Name: "org.osbuild.qemu",
+				Options: &QEMUAssemblerOptions{
+					Format:   "qcow2",
+					Filename: "disk.qcow2",
+					Size:     2147483648,
+					PTUUID:   "0x14fc63d2",
+					PTType:   "mbr",
+					Partitions: []QEMUPartition{QEMUPartition{
+						Start:    2048,
+						Bootable: true,
+						Filesystem: QEMUFilesystem{
+							Type:       "ext4",
+							UUID:       "76a22bf4-f153-4541-b6c7-0332c0dfaeac",
+							Label:      "root",
+							Mountpoint: "/",
+						},
+					}},
+				},
+			},
+			data: []byte(`{"name":"org.osbuild.qemu","options":{"format":"qcow2","filename":"disk.qcow2","size":2147483648,"ptuuid":"0x14fc63d2","pttype":"mbr","partitions":[{"start":2048,"bootable":true,"filesystem":{"type":"ext4","uuid":"76a22bf4-f153-4541-b6c7-0332c0dfaeac","label":"root","mountpoint":"/"}}]}}`),
+		},
+		{
+			name: "tar assembler empty",
+			assembler: Assembler{
+				Name:    "org.osbuild.tar",
+				Options: &TarAssemblerOptions{},
+			},
+			data: []byte(`{"name":"org.osbuild.tar","options":{"filename":"","size":0}}`),
+		},
+		{
+			name: "tar assembler full",
+			assembler: Assembler{
+				Name: "org.osbuild.tar",
+				Options: &TarAssemblerOptions{
+					Filename:    "root.tar.xz",
+					Size:        0,
+					Compression: "xz",
+				},
+			},
+			data: []byte(`{"name":"org.osbuild.tar","options":{"filename":"root.tar.xz","size":0,"compression":"xz"}}`),
+		},
+		{
+			name: "rawfs assembler empty",
+			assembler: Assembler{
+				Name:    "org.osbuild.rawfs",
+				Options: &RawFSAssemblerOptions{},
+			},
+			data: []byte(`{"name":"org.osbuild.rawfs","options":{"filename":"","root_fs_uuid":"00000000-0000-0000-0000-000000000000","size":0}}`),
+		},
+		{
+			name: "rawfs assembler full",
+			assembler: Assembler{
+				Name: "org.osbuild.rawfs",
+				Options: &RawFSAssemblerOptions{
+					Filename:           "filesystem.img",
+					RootFilesystemUUID: uuid.MustParse("76a22bf4-f153-4541-b6c7-0332c0dfaeac"),
+					Size:               2147483648,
+				},
+			},
+			data: []byte(`{"name":"org.osbuild.rawfs","options":{"filename":"filesystem.img","root_fs_uuid":"76a22bf4-f153-4541-b6c7-0332c0dfaeac","size":2147483648}}`),
+		},
+	}
+
+	assert := assert.New(t)
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assembler := &tt.assembler
+			var gotAssembler Assembler
+			err := gotAssembler.UnmarshalJSON(tt.data)
+			if tt.errorExpected {
+				assert.NotNil(err)
+				return
+			} else {
+				assert.Nil(err)
+			}
+			gotBytes, err := json.Marshal(assembler)
+			assert.Nilf(err, "Could not marshal assembler: %v", err)
+			assert.Equal(tt.data, gotBytes)
+			assert.Equal(&gotAssembler, assembler)
+		})
+	}
+}
+
+func TestNewQEMUAssembler(t *testing.T) {
+	options := &QEMUAssemblerOptions{}
+	expectedAssembler := &Assembler{
+		Name:    "org.osbuild.qemu",
+		Options: &QEMUAssemblerOptions{},
+	}
+	assert.Equal(t, expectedAssembler, NewQEMUAssembler(options))
+}
+
+func TestNewTarAssembler(t *testing.T) {
+	options := &TarAssemblerOptions{}
+	expectedAssembler := &Assembler{
+		Name:    "org.osbuild.tar",
+		Options: &TarAssemblerOptions{},
+	}
+	assert.Equal(t, expectedAssembler, NewTarAssembler(options))
+}
+
+func TestNewRawFSAssembler(t *testing.T) {
+	options := &RawFSAssemblerOptions{}
+	expectedAssembler := &Assembler{
+		Name:    "org.osbuild.rawfs",
+		Options: &RawFSAssemblerOptions{},
+	}
+	assert.Equal(t, expectedAssembler, NewRawFSAssembler(options))
+}