Adding key name to value using jq - jq

Question

I am trying to dynamically assign the key name as its value in my json
This is the json i am using:
{
"test1": "",
"test2": "",
"test3": ""
}
the result i would like to obtain looks like this:
{
"test1": "test1",
"test2": "test2",
"test3": "test3"
}
I am not familiar with jq and the closest result i got is using:
keys[] as $key | {"\($key)": "\($key)"} | .
here is the output:
{
"test1": "test1"
}
{
"test2": "test2"
}
{
"test3": "test3"
}

Answer 1

with_entries lets you manipulate .key and .value for each field. Just set one to the value of the other:
with_entries(.value = .key)
{
"test1": "test1",
"test2": "test2",
"test3": "test3"
}
Demo
Following your approach, you could collect your result objects into an array using the array constructors […] around your filter, and then add up the array's items producing one merged object. (Note that | . can be dropped as it doesn't do anything but reproduce itself, and that the string interpolation "\($key)" is just the same as $key, given $key is a string, which is the case here as object field names are always strings.)
[keys[] as $key | {($key): $key}] | add
Demo
You may also entirely drop the use of variables as there is no other context interfering:
[keys[] | {"\(.)": .}] | add
Demo
And there is a shortcut for patterns like [.[] | …] called map:
keys | map({"\(.)": .}) | add
Demo
Alternatively, you also might want to consider using reduce for an iterative manipulation, and/or keys_unsorted which acts like keys but produces the keys in the original (unsorted) order:
reduce keys_unsorted[] as $key (.; .[$key] = $key)
Demo