diff --git a/test/command_callback/ols_paths/.merlin b/test/command_callback/ols_paths/.merlin
new file mode 100644
index 0000000..e69de29
diff --git a/test/command_callback/ols_paths/node_modules/.bin/ocaml-language-server b/test/command_callback/ols_paths/node_modules/.bin/ocaml-language-server
new file mode 100644
index 0000000..e69de29
diff --git a/test/command_callback/test_ocaml_ols_callbacks.vader b/test/command_callback/test_ocaml_ols_callbacks.vader
new file mode 100644
index 0000000..2c44dbc
--- /dev/null
+++ b/test/command_callback/test_ocaml_ols_callbacks.vader
@@ -0,0 +1,54 @@
+Before:
+  Save &filetype
+  Save g:ale_ocaml_ols_executable
+  Save g:ale_ocaml_ols_use_global
+
+  let &filetype = 'ocaml'
+  unlet! g:ale_ocaml_ols_executable
+  unlet! g:ale_ocaml_ols_use_global
+
+  runtime ale_linters/ocaml/ols.vim
+
+  call ale#test#SetDirectory('/testplugin/test/command_callback')
+
+After:
+  Restore
+
+  call ale#test#RestoreDirectory()
+  call ale#linter#Reset()
+
+Execute(The language string should be correct):
+  AssertEqual 'ocaml', ale#handlers#ols#GetLanguage(bufnr(''))
+
+Execute(The default executable should be correct):
+  AssertEqual 'ocaml-language-server', ale#handlers#ols#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('ocaml-language-server') . ' --stdio',
+  \ ale#handlers#ols#GetCommand(bufnr(''))
+
+Execute(The project root should be detected correctly):
+  AssertEqual '', ale#handlers#ols#GetProjectRoot(bufnr(''))
+
+  call ale#test#SetFilename('ols_paths/file.ml')
+
+  AssertEqual
+  \ ale#path#Winify(g:dir . '/ols_paths'),
+  \ ale#handlers#ols#GetProjectRoot(bufnr(''))
+
+Execute(The local executable should be used when available):
+  call ale#test#SetFilename('ols_paths/file.ml')
+
+  AssertEqual
+  \ ale#path#Winify(g:dir . '/ols_paths/node_modules/.bin/ocaml-language-server'),
+  \ ale#handlers#ols#GetExecutable(bufnr(''))
+
+Execute(The gloabl executable should always be used when use_global is set):
+  let g:ale_ocaml_ols_use_global = 1
+  call ale#test#SetFilename('ols_paths/file.ml')
+
+  AssertEqual 'ocaml-language-server', ale#handlers#ols#GetExecutable(bufnr(''))
+
+Execute(The executable should be configurable):
+  let g:ale_ocaml_ols_executable = 'foobar'
+
+  AssertEqual 'foobar', ale#handlers#ols#GetExecutable(bufnr(''))
diff --git a/test/command_callback/test_reason_ols_callbacks.vader b/test/command_callback/test_reason_ols_callbacks.vader
new file mode 100644
index 0000000..ffe403f
--- /dev/null
+++ b/test/command_callback/test_reason_ols_callbacks.vader
@@ -0,0 +1,54 @@
+Before:
+  Save &filetype
+  Save g:ale_reason_ols_executable
+  Save g:ale_reason_ols_use_global
+
+  let &filetype = 'reason'
+  unlet! g:ale_reason_ols_executable
+  unlet! g:ale_reason_ols_use_global
+
+  runtime ale_linters/reason/ols.vim
+
+  call ale#test#SetDirectory('/testplugin/test/command_callback')
+
+After:
+  Restore
+
+  call ale#test#RestoreDirectory()
+  call ale#linter#Reset()
+
+Execute(The language string should be correct):
+  AssertEqual 'reason', ale#handlers#ols#GetLanguage(bufnr(''))
+
+Execute(The default executable should be correct):
+  AssertEqual 'ocaml-language-server', ale#handlers#ols#GetExecutable(bufnr(''))
+  AssertEqual
+  \ ale#Escape('ocaml-language-server') . ' --stdio',
+  \ ale#handlers#ols#GetCommand(bufnr(''))
+
+Execute(The project root should be detected correctly):
+  AssertEqual '', ale#handlers#ols#GetProjectRoot(bufnr(''))
+
+  call ale#test#SetFilename('ols_paths/file.re')
+
+  AssertEqual
+  \ ale#path#Winify(g:dir . '/ols_paths'),
+  \ ale#handlers#ols#GetProjectRoot(bufnr(''))
+
+Execute(The local executable should be used when available):
+  call ale#test#SetFilename('ols_paths/file.re')
+
+  AssertEqual
+  \ ale#path#Winify(g:dir . '/ols_paths/node_modules/.bin/ocaml-language-server'),
+  \ ale#handlers#ols#GetExecutable(bufnr(''))
+
+Execute(The gloabl executable should always be used when use_global is set):
+  let g:ale_reason_ols_use_global = 1
+  call ale#test#SetFilename('ols_paths/file.re')
+
+  AssertEqual 'ocaml-language-server', ale#handlers#ols#GetExecutable(bufnr(''))
+
+Execute(The executable should be configurable):
+  let g:ale_reason_ols_executable = 'foobar'
+
+  AssertEqual 'foobar', ale#handlers#ols#GetExecutable(bufnr(''))