diff --git a/test/README.markdown b/test/README.markdown
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--- /dev/null
+++ b/test/README.markdown
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+## Testing vim-gitgutter
+
+### Run the tests
+
+```sh
+$ cd test
+$ ./test.sh
+```
+
+### Add a new test
+
+1. Add new test function to `test.vim`.
+2. Add a call to the test function in `test.vim`.
+3. Run the tests.
+4. Inspect output from the new test function.  If good, copy it to `<blah>.ok`.
+5. Run the tests to ensure new test's output is verified.
+6. `rm *.out` and commit changes.
+
+### Potential test pitfalls
+
+Currently the tests are order-dependent because the sign id counter isn't reset between tests.
diff --git a/test/addLines.ok b/test/addLines.ok
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--- /dev/null
+++ b/test/addLines.ok
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+
+--- Signs ---
+Signs for fixture.txt:
+    line=2  id=3000  name=GitGutterLineAdded
diff --git a/test/fixture.txt b/test/fixture.txt
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--- /dev/null
+++ b/test/fixture.txt
@@ -0,0 +1,11 @@
+a
+b
+c
+d
+e
+f
+g
+h
+i
+j
+
diff --git a/test/modifyLines.ok b/test/modifyLines.ok
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--- /dev/null
+++ b/test/modifyLines.ok
@@ -0,0 +1,4 @@
+
+--- Signs ---
+Signs for fixture.txt:
+    line=1  id=3001  name=GitGutterLineModified
diff --git a/test/noModifications.ok b/test/noModifications.ok
new file mode 100644
index 0000000..aa8cd86
--- /dev/null
+++ b/test/noModifications.ok
@@ -0,0 +1,2 @@
+
+--- Signs ---
diff --git a/test/orphanedSigns.ok b/test/orphanedSigns.ok
new file mode 100644
index 0000000..b37ee1b
--- /dev/null
+++ b/test/orphanedSigns.ok
@@ -0,0 +1,4 @@
+
+--- Signs ---
+Signs for fixture.txt:
+    line=6  id=3005  name=GitGutterLineAdded
diff --git a/test/removeFirstLines.ok b/test/removeFirstLines.ok
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index 0000000..4249f5d
--- /dev/null
+++ b/test/removeFirstLines.ok
@@ -0,0 +1,4 @@
+
+--- Signs ---
+Signs for fixture.txt:
+    line=1  id=3003  name=GitGutterLineRemovedFirstLine
diff --git a/test/removeLines.ok b/test/removeLines.ok
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index 0000000..284b83e
--- /dev/null
+++ b/test/removeLines.ok
@@ -0,0 +1,4 @@
+
+--- Signs ---
+Signs for fixture.txt:
+    line=4  id=3002  name=GitGutterLineRemoved
diff --git a/test/test.sh b/test/test.sh
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--- /dev/null
+++ b/test/test.sh
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+#!/usr/bin/env bash
+
+rm -f *.out
+
+# Run the tests.
+vim -N -u NONE -S test.vim
+
+# Verify the outputs.
+for expected in *.ok; do
+  name=${expected%.*}
+  actual=$name.out
+  diff $expected $actual && echo "$name ok" || echo "$name failed"
+done
diff --git a/test/test.vim b/test/test.vim
new file mode 100644
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--- /dev/null
+++ b/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!
+