feat: migrate unit tests to Jest (#6353)

* config(jest): updated setup
* config(jest): update testMatch to include jsx files
* config(jest): add transformIgnorePatterns
* config(jest): update ignore files that do not work in jest yet
* config: add test:unit-jest to test script

* fix(jest): lint with eslint-plugin-jest

* refactor(jest): move unit test directory
* refactor(mocha): restore mocha tests that fail in jest

* docs(jest): update helpful scripts with test:unit-jest

test/unit/core/plugins/oas3/servers-wrapper.jsx

@@ -0,0 +1,75 @@
+
+import React from "react"
+import { mount } from "enzyme"
+import { fromJS } from "immutable"
+import ServersContainer from "core/plugins/oas3/components/servers-container"
+import Servers from "core/plugins/oas3/components/servers"
+import { Col } from "components/layout-utils"
+
+describe("<ServersContainer/>", function(){
+
+  const components = {
+    Servers,
+    Col
+  }
+  const mockedProps = {
+    specSelectors: {
+      servers() {}
+    },
+    oas3Selectors: {
+      selectedServer() {},
+      serverVariableValue() {},
+      serverEffectiveValue() {}
+    },
+    oas3Actions: {
+      setSelectedServer() {},
+      setServerVariableValue() {}
+    },
+    getComponent: c => components[c]
+  }
+
+  it("renders Servers inside ServersContainer if servers are provided", function(){
+
+    // Given
+    let props = {...mockedProps}
+    props.specSelectors = {...mockedProps.specSelectors}
+    props.specSelectors.servers = function() {return fromJS([{url: "http://server1.com"}])}
+    props.oas3Selectors = {...mockedProps.oas3Selectors}
+    props.oas3Selectors.selectedServer = function() {return "http://server1.com"}
+
+    // When
+    let wrapper = mount(<ServersContainer {...props}/>)
+
+    // Then
+    const renderedServers = wrapper.find(Servers)
+    expect(renderedServers.length).toEqual(1)
+  })
+
+  it("does not render Servers inside ServersContainer if servers are empty", function(){
+
+    // Given
+    let props = {...mockedProps}
+    props.specSelectors = {...mockedProps.specSelectors}
+    props.specSelectors.servers = function() {return fromJS([])}
+
+    // When
+    let wrapper = mount(<ServersContainer {...props}/>)
+
+    // Then
+    const renderedServers = wrapper.find(Servers)
+    expect(renderedServers.length).toEqual(0)
+  })
+
+  it("does not render Servers inside ServersContainer if servers are undefined", function(){
+
+    // Given
+    let props = {...mockedProps}
+
+    // When
+    let wrapper = mount(<ServersContainer {...props}/>)
+
+    // Then
+    const renderedServers = wrapper.find(Servers)
+    expect(renderedServers.length).toEqual(0)
+  })
+})