add tests for GreetingController

src/main/kotlin/com/example/demo/controllers/GreetingController.kt

@@ -2,6 +2,7 @@ package com.example.demo.controllers
 
 import com.example.demo.provider.html.renderProductTable
 import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.ResponseBody
 import org.springframework.web.bind.annotation.RestController
 
 @RestController
@@ -11,7 +12,8 @@ class GreetingController {
         return "Hello World!"
     }
 
-    @GetMapping("/example/html")
+    @GetMapping(value = ["/example/html"], produces = ["text/html"])
+    @ResponseBody
     fun exampleHtml(): String {
         return renderProductTable()
     }

src/test/kotlin/com/example/demo/controllers/GreetingControllerTest.kt

@@ -0,0 +1,30 @@
+package com.example.demo.controllers
+
+import org.hamcrest.core.StringContains
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest
+import org.springframework.test.web.servlet.MockMvc
+import org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get
+import org.springframework.test.web.servlet.result.MockMvcResultMatchers.content
+import org.springframework.test.web.servlet.result.MockMvcResultMatchers.status
+import kotlin.test.Test
+
+@WebMvcTest(GreetingController::class)
+class GreetingControllerTest(@Autowired val mockMvc: MockMvc) {
+
+    @Test
+    fun greetings_shouldSeeGreetingMessage() {
+        mockMvc.perform(get("/greeting"))
+            .andExpect(status().isOk)
+            .andExpect(content().contentType("text/plain;charset=UTF-8"))
+            .andExpect(content().string("Hello World!"))
+    }
+
+    @Test
+    fun exampleHtml_shouldSeeRenderedHtml() {
+        mockMvc.perform(get("/example/html"))
+            .andExpect(status().isOk)
+            .andExpect(content().contentType("text/html;charset=UTF-8"))
+            .andExpect(content().string(StringContains("Product")))
+    }
+}