diff --git a/internal/modifiers/attr_modifiers.go b/internal/modifiers/attr_wrapper.go
similarity index 100%
rename from internal/modifiers/attr_modifiers.go
rename to internal/modifiers/attr_wrapper.go
diff --git a/internal/modifiers/attr_wrapper_test.go b/internal/modifiers/attr_wrapper_test.go
new file mode 100644
index 0000000..bb9dfd1
--- /dev/null
+++ b/internal/modifiers/attr_wrapper_test.go
@@ -0,0 +1,63 @@
+package modifiers
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	tt "github.com/vingarcia/ksql/internal/testtools"
+)
+
+func TestAttrWrapper(t *testing.T) {
+	ctx := context.Background()
+
+	var scanArgs map[string]interface{}
+	var valueArgs map[string]interface{}
+	wrapper := AttrWrapper{
+		Ctx:  ctx,
+		Attr: "fakeAttr",
+		Modifier: AttrModifierMock{
+			AttrScanFn: func(ctx context.Context, opInfo OpInfo, attrPtr interface{}, dbValue interface{}) error {
+				scanArgs = map[string]interface{}{
+					"opInfo":  opInfo,
+					"attrPtr": attrPtr,
+					"dbValue": dbValue,
+				}
+				return errors.New("fakeScanErrMsg")
+			},
+			AttrValueFn: func(ctx context.Context, opInfo OpInfo, inputValue interface{}) (outputValue interface{}, _ error) {
+				valueArgs = map[string]interface{}{
+					"opInfo":     opInfo,
+					"inputValue": inputValue,
+				}
+				return "fakeOutputValue", errors.New("fakeValueErrMsg")
+			},
+		},
+		OpInfo: OpInfo{
+			Method:     "fakeMethod",
+			DriverName: "fakeDriverName",
+		},
+	}
+
+	err := wrapper.Scan("fakeDbValue")
+	tt.AssertErrContains(t, err, "fakeScanErrMsg")
+	tt.AssertEqual(t, scanArgs, map[string]interface{}{
+		"opInfo": OpInfo{
+			Method:     "fakeMethod",
+			DriverName: "fakeDriverName",
+		},
+		"attrPtr": "fakeAttr",
+		"dbValue": "fakeDbValue",
+	})
+
+	value, err := wrapper.Value()
+	tt.AssertErrContains(t, err, "fakeValueErrMsg")
+	tt.AssertEqual(t, valueArgs, map[string]interface{}{
+		"opInfo": OpInfo{
+			Method:     "fakeMethod",
+			DriverName: "fakeDriverName",
+		},
+		"inputValue": "fakeAttr",
+	})
+	tt.AssertEqual(t, value, "fakeOutputValue")
+}
diff --git a/internal/modifiers/global_modifiers_test.go b/internal/modifiers/global_modifiers_test.go
new file mode 100644
index 0000000..4607cbc
--- /dev/null
+++ b/internal/modifiers/global_modifiers_test.go
@@ -0,0 +1,45 @@
+package modifiers
+
+import (
+	"testing"
+
+	tt "github.com/vingarcia/ksql/internal/testtools"
+)
+
+func TestRegisterAttrModifier(t *testing.T) {
+	t.Run("should register new modifiers correctly", func(t *testing.T) {
+		modifier1 := AttrModifierMock{}
+		modifier2 := AttrModifierMock{}
+
+		RegisterAttrModifier("fakeModifierName1", &modifier1)
+		RegisterAttrModifier("fakeModifierName2", &modifier2)
+
+		mod, err := LoadGlobalModifier("fakeModifierName1")
+		tt.AssertNoErr(t, err)
+		tt.AssertEqual(t, mod, &modifier1)
+
+		mod, err = LoadGlobalModifier("fakeModifierName2")
+		tt.AssertNoErr(t, err)
+		tt.AssertEqual(t, mod, &modifier2)
+	})
+
+	t.Run("should panic registering a modifier and the name already exists", func(t *testing.T) {
+		modifier1 := AttrModifierMock{}
+		modifier2 := AttrModifierMock{}
+
+		RegisterAttrModifier("fakeModifierName", &modifier1)
+		panicPayload := tt.PanicHandler(func() {
+			RegisterAttrModifier("fakeModifierName", &modifier2)
+		})
+
+		err, ok := panicPayload.(error)
+		tt.AssertEqual(t, ok, true)
+		tt.AssertErrContains(t, err, "KSQL", "fakeModifierName", "name is already in use")
+	})
+
+	t.Run("should return an error when loading an inexistent modifier", func(t *testing.T) {
+		mod, err := LoadGlobalModifier("nonExistentModifier")
+		tt.AssertErrContains(t, err, "nonExistentModifier")
+		tt.AssertEqual(t, mod, nil)
+	})
+}
diff --git a/internal/modifiers/json_modifier_test.go b/internal/modifiers/json_modifier_test.go
new file mode 100644
index 0000000..968e468
--- /dev/null
+++ b/internal/modifiers/json_modifier_test.go
@@ -0,0 +1,122 @@
+package modifiers
+
+import (
+	"context"
+	"testing"
+
+	tt "github.com/vingarcia/ksql/internal/testtools"
+)
+
+func TestAttrScan(t *testing.T) {
+	ctx := context.Background()
+
+	type FakeAttr struct {
+		Foo string `json:"foo"`
+	}
+
+	tests := []struct {
+		desc               string
+		dbInput            interface{}
+		expectedValue      interface{}
+		expectErrToContain []string
+	}{
+		{
+			desc:          "should set struct to zero value if input is nil",
+			dbInput:       nil,
+			expectedValue: FakeAttr{},
+		},
+		{
+			desc:    "should work when input is a byte slice",
+			dbInput: []byte(`{"foo":"bar"}`),
+			expectedValue: FakeAttr{
+				Foo: "bar",
+			},
+		},
+		{
+			desc:    "should work when input is a string",
+			dbInput: `{"foo":"bar"}`,
+			expectedValue: FakeAttr{
+				Foo: "bar",
+			},
+		},
+		{
+			desc:               "should report error if input type is unsupported",
+			dbInput:            10,
+			expectErrToContain: []string{"unexpected type", "int"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			fakeAttr := FakeAttr{
+				Foo: "notZeroValue",
+			}
+			err := jsonModifier{}.AttrScan(ctx, OpInfo{}, &fakeAttr, test.dbInput)
+			if test.expectErrToContain != nil {
+				tt.AssertErrContains(t, err, test.expectErrToContain...)
+				t.Skip()
+			}
+
+			tt.AssertNoErr(t, err)
+			tt.AssertEqual(t, fakeAttr, test.expectedValue)
+		})
+	}
+}
+
+func TestAttrValue(t *testing.T) {
+	ctx := context.Background()
+
+	type FakeAttr struct {
+		Foo string `json:"foo"`
+	}
+
+	tests := []struct {
+		desc        string
+		dbInput     interface{}
+		opInfoInput OpInfo
+		attrValue   interface{}
+
+		expectedOutput     interface{}
+		expectErrToContain []string
+	}{
+		{
+			desc:    "should return a byte array when the driver is not sqlserver",
+			dbInput: []byte(`{"foo":"bar"}`),
+			opInfoInput: OpInfo{
+				DriverName: "notSQLServer",
+			},
+			attrValue: FakeAttr{
+				Foo: "bar",
+			},
+			expectedOutput: tt.ToJSON(t, map[string]interface{}{
+				"foo": "bar",
+			}),
+		},
+		{
+			desc:    "should return a string when the driver is sqlserver",
+			dbInput: []byte(`{"foo":"bar"}`),
+			opInfoInput: OpInfo{
+				DriverName: "sqlserver",
+			},
+			attrValue: FakeAttr{
+				Foo: "bar",
+			},
+			expectedOutput: string(tt.ToJSON(t, map[string]interface{}{
+				"foo": "bar",
+			})),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			output, err := jsonModifier{}.AttrValue(ctx, test.opInfoInput, test.attrValue)
+			if test.expectErrToContain != nil {
+				tt.AssertErrContains(t, err, test.expectErrToContain...)
+				t.Skip()
+			}
+
+			tt.AssertNoErr(t, err)
+			tt.AssertEqual(t, output, test.expectedOutput)
+		})
+	}
+}
diff --git a/internal/modifiers/mocks.go b/internal/modifiers/mocks.go
new file mode 100644
index 0000000..d023dc9
--- /dev/null
+++ b/internal/modifiers/mocks.go
@@ -0,0 +1,38 @@
+package modifiers
+
+import "context"
+
+// AttrModifierMock mocks the modifiers.AttrModifier interface
+type AttrModifierMock struct {
+	AttrScanFn func(
+		ctx context.Context,
+		opInfo OpInfo,
+		attrPtr interface{},
+		dbValue interface{},
+	) error
+
+	AttrValueFn func(
+		ctx context.Context,
+		opInfo OpInfo,
+		inputValue interface{},
+	) (outputValue interface{}, _ error)
+}
+
+// AttrScan mocks the AttrScan method
+func (a AttrModifierMock) AttrScan(
+	ctx context.Context,
+	opInfo OpInfo,
+	attrPtr interface{},
+	dbValue interface{},
+) error {
+	return a.AttrScanFn(ctx, opInfo, attrPtr, dbValue)
+}
+
+// AttrValue mocks the AttrValue method
+func (a AttrModifierMock) AttrValue(
+	ctx context.Context,
+	opInfo OpInfo,
+	inputValue interface{},
+) (outputValue interface{}, _ error) {
+	return a.AttrValueFn(ctx, opInfo, inputValue)
+}
diff --git a/internal/testtools/json.go b/internal/testtools/json.go
new file mode 100644
index 0000000..b8712bf
--- /dev/null
+++ b/internal/testtools/json.go
@@ -0,0 +1,13 @@
+package tt
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func ToJSON(t *testing.T, obj interface{}) []byte {
+	rawJSON, err := json.Marshal(obj)
+	AssertNoErr(t, err)
+
+	return rawJSON
+}