Add unit tests for IsBool converter

This commit introduces a new test file, func_is_bool_test.go, within the
pkg/ottl/ottlfuncs directory. The test file contains comprehensive unit
tests for the IsBool converter, ensuring its accuracy in type validation
for various input value scenarios.

Specifically, the tests cover:

- Native boolean values
- pcommon.ValueTypeBool objects
- Incorrect types such as integers and slices
- Error handling for type errors

pkg/ottl/ottlfuncs/func_is_bool_test.go

@@ -0,0 +1,74 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package ottlfuncs
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.opentelemetry.io/collector/pdata/pcommon"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+)
+
+func Test_IsBool(t *testing.T) {
+	tests := []struct {
+		name     string
+		value    interface{}
+		expected bool
+	}{
+		{
+			name:     "bool",
+			value:    true,
+			expected: true,
+		},
+		{
+			name:     "ValueTypeBool",
+			value:    pcommon.NewValueBool(false),
+			expected: true,
+		},
+		{
+			name:     "not bool",
+			value:    1,
+			expected: false,
+		},
+		{
+			name:     "ValueTypeSlice",
+			value:    pcommon.NewValueSlice(),
+			expected: false,
+		},
+		{
+			name:     "nil",
+			value:    nil,
+			expected: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			exprFunc := isBool[any](&ottl.StandardBoolGetter[any]{
+				Getter: func(context.Context, interface{}) (interface{}, error) {
+					return tt.value, nil
+				},
+			})
+			result, err := exprFunc(context.Background(), nil)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// nolint:errorlint
+func Test_IsBool_Error(t *testing.T) {
+	exprFunc := isBool[any](&ottl.StandardBoolGetter[any]{
+		Getter: func(context.Context, interface{}) (interface{}, error) {
+			return nil, ottl.TypeError("")
+		},
+	})
+	result, err := exprFunc(context.Background(), nil)
+	assert.Equal(t, false, result)
+	assert.Error(t, err)
+	_, ok := err.(ottl.TypeError)
+	assert.False(t, ok)
+}