spy.printf

spy.printf("format string", [arg1, arg2, ...]);

Returns the passed format string with the following replacements performed:

%n

the name of the spy ("spy" by default)

%c

the number of times the spy was called, in words ("once", "twice", etc.)

%C

a list of string representations of the calls to the spy, with each call prefixed by a newline and four spaces

%t

a comma-delimited list of this values the spy was called on

%n

the formatted value of the nth argument passed to printf

%*

a comma-delimited list of the (non-format string) arguments passed to printf

%D

a multi-line list of the arguments received by all calls to the spy

import tap from "tap";
import * as sinon from "sinon";

tap.test("spy.printf", (t) => {
  const s = sinon.spy(function hello() {
    return "world";
  });

  s();
  s();

  t.equal(s.printf("%n"), "hello", "formats spy name with %n");

  t.equal(
    s.printf("The spy %n has been called %c"),
    "The spy hello has been called twice",
    "formats spy name and call count"
  );

  t.end();
});