Add test for `WithAdditionalErrorDetail`

acme/errors.go

@@ -310,8 +310,9 @@ func (e *Error) AddSubproblems(subproblems ...Subproblem) *Error {
 // more information to the ACME client.
 func (e *Error) WithAdditionalErrorDetail() *Error {
 	// prevent internal server errors from disclosing
-	// the internal error to the client at all times.
-	if e == nil || e.Status >= 500 {
+	// the internal error to the client at all times and
+	// prevent nil pointers.
+	if e == nil || e.Status >= 500 || e.Err == nil {
 		return e
 	}
 

acme/errors_test.go

@@ -0,0 +1,55 @@
+package acme
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func mustJSON(t *testing.T, m map[string]interface{}) string {
+	t.Helper()
+
+	b, err := json.Marshal(m)
+	require.NoError(t, err)
+
+	return string(b)
+}
+
+func TestError_WithAdditionalErrorDetail(t *testing.T) {
+	internalJSON := mustJSON(t, map[string]interface{}{
+		"detail": "The server experienced an internal error",
+		"type":   "urn:ietf:params:acme:error:serverInternal",
+	})
+	malformedErr := NewError(ErrorMalformedType, "malformed error")
+	malformedErr.Err = nil
+	malformedJSON := mustJSON(t, map[string]interface{}{
+		"detail": "The request message was malformed",
+		"type":   "urn:ietf:params:acme:error:malformed",
+	})
+	withDetailJSON := mustJSON(t, map[string]interface{}{
+		"detail": "Attestation statement cannot be verified: invalid property",
+		"type":   "urn:ietf:params:acme:error:badAttestationStatement",
+	})
+	tests := []struct {
+		name string
+		err  *Error
+		want string
+	}{
+		{"internal", NewError(ErrorServerInternalType, "").WithAdditionalErrorDetail(), internalJSON},
+		{"nil err", malformedErr.WithAdditionalErrorDetail(), malformedJSON},
+		{"detailed", NewError(ErrorBadAttestationStatementType, "invalid property").WithAdditionalErrorDetail(), withDetailJSON},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			b, err := json.Marshal(tt.err)
+			require.NoError(t, err)
+
+			// tests if the additional error detail is included in the JSON representation
+			// of the ACME error. This is what is returned to ACME clients and being logged
+			// by the CA.
+			assert.JSONEq(t, tt.want, string(b))
+		})
+	}
+}