[refactor] unit tests (continued) - plugins

This commit includes some refactoring in unit tests.  As we test more plugins,
it seems unweildy to include every test class in the test_plugins.py file.  This
patch split apart all of the test plugins to their own respective files,
including the new test_plugin_calculator.py file.

tests/unit/test_plugin_calculator.py

@@ -0,0 +1,70 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# pylint: disable=missing-module-docstring
+
+from mock import Mock
+from parameterized.parameterized import parameterized
+from searx import plugins
+from tests import SearxTestCase
+from .test_utils import random_string
+
+from .test_plugins import get_search_mock
+
+
+class PluginCalculator(SearxTestCase):  # pylint: disable=missing-class-docstring
+    def setUp(self):
+        self.store = plugins.PluginStore()
+        plugin = plugins.load_and_initialize_plugin('searx.plugins.calculator', False, (None, {}))
+        self.store.register(plugin)
+
+    def test_plugin_store_init(self):
+        self.assertEqual(1, len(self.store.plugins))
+
+    def test_single_page_number_true(self):
+        request = Mock(remote_addr='127.0.0.1')
+        search = get_search_mock(query=random_string(10), pageno=2)
+        result = self.store.call(self.store.plugins, 'post_search', request, search)
+        self.assertTrue(result)
+        self.assertNotIn('calculate', search.result_container.answers)
+
+    def test_long_query_true(self):
+        request = Mock(remote_addr='127.0.0.1')
+        search = get_search_mock(query=random_string(101), pageno=1)
+        result = self.store.call(self.store.plugins, 'post_search', request, search)
+        self.assertTrue(result)
+        self.assertNotIn('calculate', search.result_container.answers)
+
+    def test_alpha_true(self):
+        request = Mock(remote_addr='127.0.0.1')
+        search = get_search_mock(query=random_string(10), pageno=1)
+        result = self.store.call(self.store.plugins, 'post_search', request, search)
+        self.assertTrue(result)
+        self.assertNotIn('calculate', search.result_container.answers)
+
+    @parameterized.expand(
+        [
+            "1+1",
+            "1-1",
+            "1*1",
+            "1/1",
+            "1**1",
+            "1^1",
+        ]
+    )
+    def test_int_operations(self, operation):
+        request = Mock(remote_addr='127.0.0.1')
+        search = get_search_mock(query=operation, pageno=1)
+        result = self.store.call(self.store.plugins, 'post_search', request, search)
+        self.assertTrue(result)
+        self.assertIn('calculate', search.result_container.answers)
+
+    @parameterized.expand(
+        [
+            "1/0",
+        ]
+    )
+    def test_invalid_operations(self, operation):
+        request = Mock(remote_addr='127.0.0.1')
+        search = get_search_mock(query=operation, pageno=1)
+        result = self.store.call(self.store.plugins, 'post_search', request, search)
+        self.assertTrue(result)
+        self.assertNotIn('calculate', search.result_container.answers)