rails3's default unit tests is not working

When I try to execute default unit tests which have been created with my
models, I get following errors.

CASE 1)
My default unit test file content;

require 'test_helper'
class UserTest < ActiveSupport::TestCase
   # Replace this with your real tests.
   test "the truth" do
       assert true
   end
end

Commands that I executed;

rake db:migrate
rake db:test:load
rake test:units --trace

(in /home/mustafakyr/Code/trunk/MyProject)
** Invoke test:units (first_time)
** Invoke test:prepare (first_time)
** Invoke db:test:prepare (first_time)
** Invoke db:abort_if_pending_migrations (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:abort_if_pending_migrations
** Execute db:test:prepare
** Invoke db:test:load (first_time)
** Invoke db:test:purge (first_time)
** Invoke environment
** Execute db:test:purge
** Execute db:test:load
** Invoke db:schema:load (first_time)
** Invoke environment
** Execute db:schema:load
** Execute test:prepare
** Execute test:units
test/unit/user_test.rb:5:in `test': unknown command 't' (ArgumentError)
  from test/unit/user_test.rb:5:in `<class:UserTest>'
  from test/unit/user_test.rb:3:in `<top (required)>'
  from /usr/local/lib/ruby/1.9.1/rake/rake_test_loader.rb:5:in `load'
  from /usr/local/lib/ruby/1.9.1/rake/rake_test_loader.rb:5:in `block in
<main>'
  from /usr/local/lib/ruby/1.9.1/rake/rake_test_loader.rb:5:in `each'
  from /usr/local/lib/ruby/1.9.1/rake/rake_test_loader.rb:5:in `<main>'
rake aborted!
Command failed with status (1): [/usr/local/bin/ruby -I"lib:test"
"/usr/loc...]
/usr/local/lib/ruby/1.9.1/rake.rb:993:in `block in sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1008:in `call'
/usr/local/lib/ruby/1.9.1/rake.rb:1008:in `sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1092:in `sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1027:in `ruby'
/usr/local/lib/ruby/1.9.1/rake.rb:1092:in `ruby'
/usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.3/lib/rails/test_unit/testing.rake:26:in
`block (2 levels) in define'
/usr/local/lib/ruby/1.9.1/rake.rb:1110:in `verbose'
/usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.3/lib/rails/test_unit/testing.rake:11:in
`block in define'
/usr/local/lib/ruby/1.9.1/rake.rb:634:in `call'
/usr/local/lib/ruby/1.9.1/rake.rb:634:in `block in execute'
/usr/local/lib/ruby/1.9.1/rake.rb:629:in `each'
/usr/local/lib/ruby/1.9.1/rake.rb:629:in `execute'
/usr/local/lib/ruby/1.9.1/rake.rb:595:in `block in
invoke_with_call_chain'
/usr/local/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/usr/local/lib/ruby/1.9.1/rake.rb:588:in `invoke_with_call_chain'
/usr/local/lib/ruby/1.9.1/rake.rb:581:in `invoke'
/usr/local/lib/ruby/1.9.1/rake.rb:2041:in `invoke_task'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `block (2 levels) in
top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `each'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `block in top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/usr/local/lib/ruby/1.9.1/rake.rb:2013:in `top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:1992:in `run'
/usr/local/bin/rake:31:in `<main>

CASE 2)
Then when I use following unit test file it is working, but when I get
an failure with test I get "rake aborted!" error.

My own unit test content;

require 'test_helper'
class UserTest < ActiveSupport::TestCase
   # Replace this with your real tests.
   def test
       assert false
   end
end

Commands that I executed;

rake test:units --trace

(in /home/mustafakyr/Code/trunk/MyProject)
** Invoke test:units (first_time)
** Invoke test:prepare (first_time)
** Invoke db:test:prepare (first_time)
** Invoke db:abort_if_pending_migrations (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:abort_if_pending_migrations
** Execute db:test:prepare
** Invoke db:test:load (first_time)
** Invoke db:test:purge (first_time)
** Invoke environment
** Execute db:test:purge
** Execute db:test:load
** Invoke db:schema:load (first_time)
** Invoke environment
** Execute db:schema:load
** Execute test:prepare
** Execute test:units
Loaded suite /usr/local/lib/ruby/1.9.1/rake/rake_test_loader
Started
F
Finished in 0.115924 seconds.

  1) Failure:
test(UserTest) [test/unit/user_test.rb:6]:
Failed assertion, no message given.

1 tests, 1 assertions, 1 failures, 0 errors, 0 skips

Test run options: --seed 43445
rake aborted!
Command failed with status (1): [/usr/local/bin/ruby -I"lib:test"
"/usr/loc...]
/usr/local/lib/ruby/1.9.1/rake.rb:993:in `block in sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1008:in `call'
/usr/local/lib/ruby/1.9.1/rake.rb:1008:in `sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1092:in `sh'
/usr/local/lib/ruby/1.9.1/rake.rb:1027:in `ruby'
/usr/local/lib/ruby/1.9.1/rake.rb:1092:in `ruby'
/usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.3/lib/rails/test_unit/testing.rake:26:in
`block (2 levels) in define'
/usr/local/lib/ruby/1.9.1/rake.rb:1110:in `verbose'
/usr/local/lib/ruby/gems/1.9.1/gems/railties-3.0.3/lib/rails/test_unit/testing.rake:11:in
`block in define'
/usr/local/lib/ruby/1.9.1/rake.rb:634:in `call'
/usr/local/lib/ruby/1.9.1/rake.rb:634:in `block in execute'
/usr/local/lib/ruby/1.9.1/rake.rb:629:in `each'
/usr/local/lib/ruby/1.9.1/rake.rb:629:in `execute'
/usr/local/lib/ruby/1.9.1/rake.rb:595:in `block in
invoke_with_call_chain'
/usr/local/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
/usr/local/lib/ruby/1.9.1/rake.rb:588:in `invoke_with_call_chain'
/usr/local/lib/ruby/1.9.1/rake.rb:581:in `invoke'
/usr/local/lib/ruby/1.9.1/rake.rb:2041:in `invoke_task'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `block (2 levels) in
top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `each'
/usr/local/lib/ruby/1.9.1/rake.rb:2019:in `block in top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/usr/local/lib/ruby/1.9.1/rake.rb:2013:in `top_level'
/usr/local/lib/ruby/1.9.1/rake.rb:1992:in `run'
/usr/local/bin/rake:31:in `<main>'

gem env

RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.7
  - RUBY VERSION: 1.9.2 (2010-12-25 patchlevel 136) [i686-linux]
  - INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/1.9.1
  - RUBY EXECUTABLE: /usr/local/bin/ruby
  - EXECUTABLE DIRECTORY: /usr/local/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-linux
  - GEM PATHS:
     - /usr/local/lib/ruby/gems/1.9.1
     - /home/mustafakyr/.gem/ruby/1.9.1
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

gem list

*** LOCAL GEMS ***

abstract (1.0.0)
actionmailer (3.0.3)
actionpack (3.0.3)
activemodel (3.0.3)
activerecord (3.0.3)
activeresource (3.0.3)
activesupport (3.0.3)
arel (2.0.6)
authlogic (2.1.6)
builder (2.1.2)
bundler (1.0.7)
cgi_multipart_eof_fix (2.5.0)
daemon_controller (0.2.5)
daemons (1.1.0)
diff-lcs (1.1.2)
erubis (2.6.6)
eventmachine (0.12.10)
extlib (0.9.15)
fastthread (1.0.7)
ffi (1.0.4)
file-tail (1.0.5)
gem_plugin (0.2.3)
gga4r (0.9.2)
gravatar (1.0)
haml (3.0.25)
highline (1.6.1)
i18n (0.5.0)
mail (2.2.13)
mime-types (1.16)
minitest (1.6.0)
mysql (2.8.1)
mysql2 (0.2.6)
passenger (3.0.2)
pg (0.10.0)
polyglot (0.3.1)
rack (1.2.1)
rack-mount (0.6.13)
rack-test (0.5.6)
rails (3.0.3)
railties (3.0.3)
rake (0.8.7)
rdoc (2.5.8)
rubygems-update (1.4.1)
scaffold (0.0.3)
spruz (0.2.2)
sqlite3 (0.1.1)
sqlite3-ruby (1.3.2)
templater (1.0.0)
test-unit (2.1.2)
thin (1.2.7)
thor (0.14.6)
treetop (1.4.9)
tzinfo (0.3.23)

My default fixture file content;

# This model initially had no columns defined. If you add columns to
the
# model remove the '{}' from the fixture names and add the columns
immediately
# below each fixture, per the syntax in the comments below