Add errdefs package

Providers should use this package so the virtual kubelet core
controllers can understand the errors produced from the provider code.

errdefs/notfound_test.go

@@ -0,0 +1,80 @@
+package errdefs
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"gotest.tools/assert"
+	"gotest.tools/assert/cmp"
+)
+
+type testingNotFoundError bool
+
+func (e testingNotFoundError) Error() string {
+	return fmt.Sprintf("%v", bool(e))
+}
+
+func (e testingNotFoundError) NotFound() bool {
+	return bool(e)
+}
+
+func TestIsNotFound(t *testing.T) {
+	type testCase struct {
+		name      string
+		err       error
+		xMsg      string
+		xNotFound bool
+	}
+
+	for _, c := range []testCase{
+		{
+			name:      "NotFoundf",
+			err:       NotFoundf("%s not found", "foo"),
+			xMsg:      "foo not found",
+			xNotFound: true,
+		},
+		{
+			name:      "AsNotFound",
+			err:       AsNotFound(errors.New("this is a test")),
+			xMsg:      "this is a test",
+			xNotFound: true,
+		},
+		{
+			name:      "AsNotFoundWithNil",
+			err:       AsNotFound(nil),
+			xMsg:      "",
+			xNotFound: false,
+		},
+		{
+			name:      "nilError",
+			err:       nil,
+			xMsg:      "",
+			xNotFound: false,
+		},
+		{
+			name:      "customNotFoundFalse",
+			err:       testingNotFoundError(false),
+			xMsg:      "false",
+			xNotFound: false,
+		},
+		{
+			name:      "customNotFoundTrue",
+			err:       testingNotFoundError(true),
+			xMsg:      "true",
+			xNotFound: true,
+		},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			assert.Check(t, cmp.Equal(IsNotFound(c.err), c.xNotFound))
+			if c.err != nil {
+				assert.Check(t, cmp.Equal(c.err.Error(), c.xMsg))
+			}
+		})
+	}
+}
+
+func TestNotFoundCause(t *testing.T) {
+	err := errors.New("test")
+	assert.Equal(t, (&notFoundError{err}).Cause(), err)
+}