@@ -69,6 +69,53 @@ for the error code should be added to the `doc/api/errors.md` file. This will
6969give users a place to go to easily look up the meaning of individual error
7070codes.
7171
72+ ## Testing new errors
73+
74+ When adding a new error, corresponding test(s) for the error message
75+ formatting may also be required. If the messasge for the error is a
76+ constant string then no test is required for the error message formatting
77+ as we can trust the error helper implementation. An example of this kind of
78+ error would be:
79+
80+ ``` js
81+ E (' ERR_SOCKET_ALREADY_BOUND' ' Socket is already bound'
82+ ```
83+
84+ If the error message is not a constant string then tests to validate
85+ the formatting of the message based on the parameters used when
86+ creating the error should be added to
87+ ` test/parallel/test-internal-errors.js ` . These tests should validate
88+ all of the different ways parameters can be used to generate the final
89+ message string. A simple example is:
90+
91+ ``` js
92+ // Test ERR_TLS_CERT_ALTNAME_INVALID
93+ assert .strictEqual (
94+ errors .message (' ERR_TLS_CERT_ALTNAME_INVALID' ' altname'
95+ ' Hostname/IP does not match certificate\' s altnames: altname'
96+ ```
97+
98+ In addition, there should also be tests which validate the use of the
99+ error based on where it is used in the codebase. For these tests, except in
100+ special cases, they should only validate that the expected code is received
101+ and NOT validate the message. This will reduce the amount of test change
102+ required when the message for an error changes.
103+
104+ For example:
105+
106+ ``` js
107+ assert .throws (() => {
108+ socket .bind ();
109+ }, common .expectsError ({
110+ code: ' ERR_SOCKET_ALREADY_BOUND'
111+ type: Error
112+ }));
113+ ```
114+
115+ Avoid changing the format of the message after the error has been created.
116+ If it does make sense to do this for some reason, then additional tests
117+ validating the formatting of the error message for those cases will
118+ likely be required.
72119
73120## API
74121
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