"go test -cpuprofile" does not generate a full trace - go

Question

Issue
I have a go package, with a test suite.
When I run the test suite for this package, the total runtime is ~ 7 seconds :
$ go test ./mydbpackage/ -count 1
ok mymodule/mydbpackage 7.253s
However, when I add a -cpuprofile=cpu.out option, the sampling does not cover the whole run :
$ go test ./mydbpackage/ -count 1 -cpuprofile=cpu.out
ok mymodule/mydbpackage 7.029s
$ go tool pprof -text -cum cpu.out
File: mydbpackage.test
Type: cpu
Time: Aug 6, 2020 at 9:42am (CEST)
Duration: 5.22s, Total samples = 780ms (14.95%) # <--- depending on the runs, I get 400ms to 1s
Showing nodes accounting for 780ms, 100% of 780ms total
flat flat% sum% cum cum%
0 0% 0% 440ms 56.41% testing.tRunner
10ms 1.28% 1.28% 220ms 28.21% database/sql.withLock
10ms 1.28% 2.56% 180ms 23.08% runtime.findrunnable
0 0% 2.56% 180ms 23.08% runtime.mcall
...
Looking at the collected samples :
# sample from another run :
$ go tool pprof -traces cpu.out | grep "ms " # get the first line of each sample
10ms runtime.nanotime
10ms fmt.(*readRune).ReadRune
30ms syscall.Syscall
10ms runtime.scanobject
10ms runtime.gentraceback
...
# 98 samples collected, for a total sum of 1.12s
The issue I see is : for some reason, the sampling profiler stops collecting samples, or is blocked/slowed down at some point.
Context
go version is 1.14.6, platform is linux/amd64
$ go version
go version go1.14.6 linux/amd64
This package contains code that interact with a database, and the tests are run against a live postgresql server.
One thing I tried : t.Skip() internally calls runtime.Goexit(), so I replaced calls to t.Skip and variants with a simple return ; but it didn't change the outcome.
Question
Why aren't more samples collected ? I there some known pattern that blocks/slows down the sampler, or terminates the sampler earlier than it should ?

Answer 1

#Volker guided me to the answer in his comments :
-cpuprofile creates a profile in which only goroutines actively using the CPU are sampled.
In my use case : my go code spends a lot of time waiting for the answers of the postgresql server.
Generating a trace using go test -trace=trace.out, and then extracting a network blocking profile using go tool trace -pprof=net trace.out > network.out yielded much more relevant information.
For reference, on top of opening the complete trace using go tool trace trace.out, here are the values you can pass to -pprof= :
from go tool trace docs :
net: network blocking profile
sync: synchronization blocking profile
syscall: syscall blocking profile
sched: scheduler latency profile