CheckHealth

- Use execute() instead of redir
- Fixed logic on suboptimal pyenv/virtualenv checks.
- Move system calls from strings to lists. Fixes #5218
- Add highlighting
- Automatically discover health checkers
- Add tests

Helped-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Helped-by: Tommy Allen <tommy@esdf.io>

Closes #4932

test/functional/plugin/health_spec.lua

@@ -0,0 +1,58 @@
+local helpers = require('test.functional.helpers')(after_each)
+local plugin_helpers = require('test.functional.plugin.helpers')
+
+describe('health.vim', function()
+  before_each(function()
+    plugin_helpers.reset()
+  end)
+
+  it('should echo the results when using the basic functions', function()
+    helpers.execute("call health#report_start('Foo')")
+    local report = helpers.redir_exec([[call health#report_start('Check Bar')]])
+      .. helpers.redir_exec([[call health#report_ok('Bar status')]])
+      .. helpers.redir_exec([[call health#report_ok('Other Bar status')]])
+      .. helpers.redir_exec([[call health#report_warn('Zub')]])
+      .. helpers.redir_exec([[call health#report_start('Baz')]])
+      .. helpers.redir_exec([[call health#report_warn('Zim', ['suggestion 1', 'suggestion 2'])]])
+
+    local expected_contents = {
+      'Checking: Check Bar',
+      'SUCCESS: Bar status',
+      'WARNING: Zub',
+      'SUGGESTIONS:',
+      '- suggestion 1',
+      '- suggestion 2'
+    }
+
+    for _, content in ipairs(expected_contents) do
+      assert(string.find(report, content))
+    end
+  end)
+
+
+  describe('CheckHealth', function()
+    -- Run the health check and store important results
+    -- Run it here because it may take awhile to complete, depending on the system
+    helpers.execute([[CheckHealth!]])
+    local report = helpers.curbuf_contents()
+    local health_checkers = helpers.redir_exec("echo g:health_checkers")
+
+    it('should find the default checker upon execution', function()
+      assert(string.find(health_checkers, "'health#nvim#check': v:true"))
+    end)
+
+    it('should alert the user that health#nvim#check is running', function()
+      assert(string.find(report, '# Checking health'))
+      assert(string.find(report, 'Checker health#nvim#check says:'))
+      assert(string.find(report, 'Checking:'))
+    end)
+  end)
+
+  it('should allow users to disable checkers', function()
+    helpers.execute("call health#disable_checker('health#nvim#check')")
+    helpers.execute("CheckHealth!")
+    local health_checkers = helpers.redir_exec("echo g:health_checkers")
+
+    assert(string.find(health_checkers, "'health#nvim#check': v:false"))
+  end)
+end)