Add basic tests.

test/test.vim

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+set runtimepath+=../
+source ../plugin/gitgutter.vim
+
+
+function! s:setup()
+  call system('git checkout fixture.txt')
+  edit! fixture.txt
+  sign unplace *
+endfunction
+
+function! s:dumpSigns(filename)
+  execute 'redir! > ' a:filename.'.out'
+    silent execute 'sign place'
+  redir END
+endfunction
+
+
+"
+" The tests.
+"
+
+function! s:testNoModifications()
+  call s:setup()
+  call s:dumpSigns('noModifications')
+endfunction
+
+function! s:testAddLines()
+  call s:setup()
+  normal ggo*
+  write
+  call s:dumpSigns('addLines')
+endfunction
+
+function! s:testModifyLines()
+  call s:setup()
+  normal ggi*
+  write
+  call s:dumpSigns('modifyLines')
+endfunction
+
+function! s:testRemoveLines()
+  call s:setup()
+  execute '5d'
+  write
+  call s:dumpSigns('removeLines')
+endfunction
+
+function! s:testRemoveFirstLines()
+  call s:setup()
+  execute '1d'
+  write
+  call s:dumpSigns('removeFirstLines')
+endfunction
+
+function! s:testOrphanedSigns()
+  call s:setup()
+  execute "normal 5GoX\<CR>Y"
+  write
+  execute '6d'
+  write
+  call s:dumpSigns('orphanedSigns')
+endfunction
+
+"
+" Execute the tests.
+"
+
+call s:testNoModifications()
+call s:testAddLines()
+call s:testModifyLines()
+call s:testRemoveLines()
+call s:testRemoveFirstLines()
+call s:testOrphanedSigns()
+
+
+"
+" Cleanup.
+"
+
+call system('git checkout fixture.txt')
+quit!
+