Add errdefs package

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

errdefs/invalid_test.go

@@ -0,0 +1,80 @@
+package errdefs
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"gotest.tools/assert"
+	"gotest.tools/assert/cmp"
+)
+
+type testingInvalidInputError bool
+
+func (e testingInvalidInputError) Error() string {
+	return fmt.Sprintf("%v", bool(e))
+}
+
+func (e testingInvalidInputError) InvalidInput() bool {
+	return bool(e)
+}
+
+func TestIsInvalidInput(t *testing.T) {
+	type testCase struct {
+		name          string
+		err           error
+		xMsg          string
+		xInvalidInput bool
+	}
+
+	for _, c := range []testCase{
+		{
+			name:          "InvalidInputf",
+			err:           InvalidInputf("%s not found", "foo"),
+			xMsg:          "foo not found",
+			xInvalidInput: true,
+		},
+		{
+			name:          "AsInvalidInput",
+			err:           AsInvalidInput(errors.New("this is a test")),
+			xMsg:          "this is a test",
+			xInvalidInput: true,
+		},
+		{
+			name:          "AsInvalidInputWithNil",
+			err:           AsInvalidInput(nil),
+			xMsg:          "",
+			xInvalidInput: false,
+		},
+		{
+			name:          "nilError",
+			err:           nil,
+			xMsg:          "",
+			xInvalidInput: false,
+		},
+		{
+			name:          "customInvalidInputFalse",
+			err:           testingInvalidInputError(false),
+			xMsg:          "false",
+			xInvalidInput: false,
+		},
+		{
+			name:          "customInvalidInputTrue",
+			err:           testingInvalidInputError(true),
+			xMsg:          "true",
+			xInvalidInput: true,
+		},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			assert.Check(t, cmp.Equal(IsInvalidInput(c.err), c.xInvalidInput))
+			if c.err != nil {
+				assert.Check(t, cmp.Equal(c.err.Error(), c.xMsg))
+			}
+		})
+	}
+}
+
+func TestInvalidInputCause(t *testing.T) {
+	err := errors.New("test")
+	assert.Equal(t, (&invalidInputError{err}).Cause(), err)
+}