Context
#1614 (comment)

In order to gain full code coverage, a test was added to show current expected behavior around what happens if a search param is set twice.

nock('http://example.test')
    .get('/')
    .query({ foo: 'bar' })
    .query({ foo: 'baz' })
    .reply()

Current behavior prefers the first value and silently ignores any subsequent values. This example will match http://example.test?foo=bar.

This is confusing and probably hides unintended bugs by users.

Alternatives

Interceptor.query should throw an error if a duplicate key is provided with a clear error message.
The "key" being checked should be the value returned by formatQueryValue instead of the input key.

The new test from #1614 should be updated test the new expected behavior.