Bats testing command output not completely captured

Context

While testing a keepass2 installation procedure using bats testing in bash, I noticed that the output of a command in terminal differs from the output that is captured in a bats test. In terminal the command keepass2 --version returns:

Gtk-Message: 15:29:44.377: Failed to load module "canberra-gtk-module"
KeePass 2.45
Copyright © 2003-2020 Dominik Reichl

Whereas the test output of the following test:

@test "Checking keepass2 version responds with Failed to load module canberra-gtk-module." {
    COMMAND_OUTPUT=$(keepass2 --version)

    EXPECTED_OUTPUT='Gtk-Message: 15:29:44.377: Failed to load module "canberra-gtk-module"
KeePass 2.45
Copyright © 2003-2020 Dominik Reichl'

    assert_equal "$COMMAND_OUTPUT" "$EXPECTED_OUTPUT"
}

is:

✗ Checking keepass2 version does not respond with Failed to load module canberra-gtk-module.
   (from function `assert_equal' in file test/post_setup/../../test/libs/bats-assert/src/assert.bash, line 91,
    in test file test/post_setup/test_apt_install_keepass2_postsetup.bats, line 68)
     `assert_equal "$COMMAND_OUTPUT" "$EXPECTED_OUTPUT"' failed
   Gtk-Message: 15:51:27.775: Failed to load module "canberra-gtk-module"
   /home/a/Documents/git/Productivity-setup/test/post_setup/../../test/libs/bats-assert/src/assert.bash: line 65: [: KeePass 2.45
   Copyright © 2003-2020 Dominik Reichl: binary operator expected
   
   -- values do not equal --
   expected (3 lines):
     Gtk-Message: 15:29:44.377: Failed to load module "canberra-gtk-module"
     KeePass 2.45
     Copyright © 2003-2020 Dominik Reichl
   actual (2 lines):
     KeePass 2.45
     Copyright © 2003-2020 Dominik Reichl
   --

So the bats test thinks the output of the command only contains the last 2 lines of the command line output of the same command, whereas I would expect bats to capture the full 3 lines of output that I see in the command line when running keepass2 --version.

Question

How can I capture the Gtk-Message: 15:29:44.377: Failed to load module "canberra-gtk-module" line that is shown in the command line for command keepass2 --version, in the bats test?