1 files changed, 40 insertions, 0 deletions
diff --git a/errors_test.go b/errors_test.go
new file mode 100644
index 0000000..c39cf67
--- /dev/null
+++ b/errors_test.go
@@ -0,0 +1,40 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package oblast
+
+import (
+	"errors"
+	"testing"
+
+	"go.xyrillian.de/oblast/internal/assert"
+)
+
+type fooError struct{}
+type barError struct{}
+type bazError struct{}
+
+func (fooError) Error() string { return "foo" }
+func (barError) Error() string { return "bar" }
+func (bazError) Error() string { return "baz" }
+
+func TestIOError(t *testing.T) {
+	err := newIOError(nil, "File.Close", nil)
+	assert.Equal(t, err == nil, true)
+
+	err = newIOError(fooError{}, "File.Close", nil)
+	assert.ErrEqual(t, err, "foo")
+	assert.DeepEqual(t, err, error(fooError{})) // check for no wrapping in type ioError without cleanup error
+
+	err = newIOError(nil, "File.Close", barError{})
+	assert.ErrEqual(t, err, "during File.Close(): bar")
+	assert.Equal(t, errors.Is(err, fooError{}), false)
+	assert.Equal(t, errors.Is(err, barError{}), true)
+	assert.Equal(t, errors.Is(err, bazError{}), false)
+
+	err = newIOError(fooError{}, "File.Close", barError{})
+	assert.ErrEqual(t, err, "foo (additional error during File.Close(): bar)")
+	assert.Equal(t, errors.Is(err, fooError{}), true)
+	assert.Equal(t, errors.Is(err, barError{}), true)
+	assert.Equal(t, errors.Is(err, bazError{}), false)
+}