test.each: %s is not substituted for non-string values in the test title

[kjanat]

What version of Bun is running?

1.3.14+0d9b296a

What platform is your computer?

Linux 7.1.6-1-MANJARO x86_64 GNU/Linux

What steps can reproduce the bug?

In a test.each / describe.each title, %s is substituted only when the value at that
position is already a string. A number leaves the literal %s in the name.

import { expect, test } from 'bun:test';

test.each(['alpha'])('string via %s: %s', (v) => expect(v).toBeDefined());
test.each([1])('integer via %s: %s', (v) => expect(v).toBeDefined());
test.each([0.8])('float via %s: %s', (v) => expect(v).toBeDefined());

// Per argument, not per row: the string substitutes and the number beside it does not.
test.each([['x', 1]])('mixed tuple via %s: %s then %s', (a, b) => expect([a, b]).toBeDefined());

// The other specifiers, for comparison.
test.each([[1, 2]])('integers via %i: %i and %i', (a, b) => expect([a, b]).toBeDefined());
test.each([0.8])('float via %i: %i', (v) => expect(v).toBeDefined());
test.each([0.8])('float via %d: %d', (v) => expect(v).toBeDefined());
test.each([0.8])('float via %f: %f', (v) => expect(v).toBeDefined());
test.each([0.8])('float via %p: %p', (v) => expect(v).toBeDefined());

The default reporter prints no per-test names when stdout is not a terminal, so the resolved
titles are easiest to read out of the junit reporter:

bun test --reporter-outfile /dev/stdout --reporter junit repro.test.ts | grep 'testcase name'

What is the expected behavior?

Jest documents %s as "String" and formats titles through util.format, where %s
stringifies any value (util.format('%s', 1) is '1'). All nine titles above should carry
their value.

What do you see instead?

table value	specifier	resulting title
'alpha'	%s	string via %s: alpha
1	%s	integer via %s: %s
0.8	%s	float via %s: %s
['x', 1]	%s twice	mixed tuple via %s: x then %s
[1, 2]	%i	integers via %i: 1 and 2
0.8	%i	float via %i: %i
0.8	%d	float via %d: 0.8
0.8	%f	float via %f: 0.8
0.8	%p	float via %p: 0.8

Two things follow. The substitution is decided per argument rather than per row: in the mixed
tuple the string is replaced and the number in the same title is not. And each specifier is
gated on its own type, %s on string and %i on integer, where %d, %f and %p accept
both.

Additional information

A table of numeric cases produces N tests sharing one title, which makes them
indistinguishable in a failure list and gives reporters keyed on test names (junit, CI
annotations, flake tracking) repeated identical entries:

✓ walking flight slide_ladder > a sim %s m below its foot is not held up by it
✓ walking flight slide_ladder > a sim %s m below its foot is not held up by it
✓ walking flight slide_ladder > a sim %s m below its foot is not held up by it

Workaround: use %d for numeric columns, which handles integers and floats, or convert the
column to a string before it reaches the title.

Related but distinct, both closed: #23206 ($name interpolation adds quotes) and #20566
(object-syntax placeholders not replaced).

[robobun]

Reproduced on 1.4.0: %s is only substituted for string values and %i only for integral numbers, so numeric table values leave the literal specifier in the title (src/runtime/test_runner/jest.rs, format_label gates each specifier on the value type before substituting).

A fix for this is already up in #32817 (item 3 there): %s accepts any value and %i truncates non-integral numbers per parseInt semantics, matching util.format. Tracking there.