Questions:
Do we all have an interview ? 100% of applicants ?
Is it always the day of the test ?
Nop. Minors don't have an interview.
All adult applicants are required to have a "Program Integrity" interview.
There is NO one rule for all minors. Minors MAY be interviewed. It appears that minors 14 and older are ordinarily interviewed BUT this is perfunctory and ordinarily happens when the minor appears for the Oath ceremony, apparently during the process of checking in to take the Oath.
Generally there is no interview for a minor under the age of 14, and such a minor does NOT need to attend an oath ceremony. Instruction guide for applications for a minor, however, state that "
the minor may be asked to come to the IRCC office for a review of the original documents submitted in support of the application, as well as all passports and travel documents relevant to the five (5) year period immediately before the application or since the minor became a permanent resident. See
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/guide-0403-citizenship-minors-subsection-5-1.html
That is basically a brief description of only PART of the Program Integrity Interview. For full description of the PI interview see
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship/admininistration/decisions/interviewing-adult-applicants.html
Generally the PI interview is the day of the test (and even for those exempt from the test, it is generally scheduled attendant a test event). Many might be interested to read and consider the differences between
the PI interview, which all adult applicants must attend, and an "In-depth residence interview" which MAY be required, which is also discussed at the linked web page.
The PDI for interviewing minors applying for citizenship can be seen here:
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship/grant/conducting-interviews-hearings-minors-applications-received-case-processing-centre-sydney-on-after-june-11-2015.html
(Again, applicant under 14 are generally NOT interviewed, and to the extent that minors 14 or older are interviewed, that is ordinarily attendant their appearance for the oath ceremony.)
General caution about current IRCC information in its PDIs:
However, it is worth noting that the link (not the reference, but the link) to this PDI has been removed from the IRCC web page with links for citizenship decision making PDIs . . . see
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship/admininistration/decisions.html
And, in turn, this page of PDI links for citizenship decision making is NO longer easily reached by a link from the general citizenship links IRCC provides. see
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/canadian-citizenship.html
Moreover, the PDIs do not necessarily reflect current policy or practice. The system is, to be frank, a mess. It is poorly maintained, poorly organized, and fails to offer much real transparency. Most information found in the PDIs is readily confirmed by anecdotal experiences reported in this forum and is otherwise consistent with the statutory provisions. But not all anecdotal reports are consistent, and to the extent the PDI describes internal procedures and related policy, and practices, which are not clearly confirmed by reliable anecdotal reporting, it can be difficult to know how much one can rely on any information in a PDI that is not otherwise also affirmatively stated in other IRCC sources.
