Refactor handler_test tests into subtests to reduce repetition (#3003)

* refactor handler_test tests into subtests to reduce repetition

* provide testing.T to the handler

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

instrumentation/net/http/otelhttp/handler_test.go

@@ -18,6 +18,7 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -26,56 +27,72 @@ import (
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 )
 
-func TestResponseWriterImplementsFlusher(t *testing.T) {
-	h := otelhttp.NewHandler(
-		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			assert.Implements(t, (*http.Flusher)(nil), w)
-		}), "test_handler",
-	)
+func TestHandler(t *testing.T) {
+	testCases := []struct {
+		name               string
+		handler            func(*testing.T) http.Handler
+		requestBody        io.Reader
+		expectedStatusCode int
+	}{
+		{
+			name: "implements flusher",
+			handler: func(t *testing.T) http.Handler {
+				return otelhttp.NewHandler(
+					http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+						assert.Implements(t, (*http.Flusher)(nil), w)
+					}), "test_handler",
+				)
+			},
+			expectedStatusCode: 200,
+		},
+		{
+			name: "succeeds",
+			handler: func(t *testing.T) http.Handler {
+				return otelhttp.NewHandler(
+					http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+						assert.NotNil(t, r.Body)
 
-	r, err := http.NewRequest(http.MethodGet, "http://localhost/", nil)
-	require.NoError(t, err)
+						b, err := io.ReadAll(r.Body)
+						assert.NoError(t, err)
+						assert.Equal(t, "hello world", string(b))
+					}), "test_handler",
+				)
+			},
+			requestBody:        strings.NewReader("hello world"),
+			expectedStatusCode: 200,
+		},
+		{
+			name: "succeeds with a nil body",
+			handler: func(t *testing.T) http.Handler {
+				return otelhttp.NewHandler(
+					http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+						assert.Nil(t, r.Body)
+					}), "test_handler",
+				)
+			},
+			expectedStatusCode: 200,
+		},
+		{
+			name: "succeeds with an http.NoBody",
+			handler: func(t *testing.T) http.Handler {
+				return otelhttp.NewHandler(
+					http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+						assert.Equal(t, http.NoBody, r.Body)
+					}), "test_handler",
+				)
+			},
+			requestBody:        http.NoBody,
+			expectedStatusCode: 200,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			r, err := http.NewRequest(http.MethodGet, "http://localhost/", tc.requestBody)
+			require.NoError(t, err)
 
-	h.ServeHTTP(httptest.NewRecorder(), r)
-}
-
-// This use case is important as we make sure the body isn't mutated
-// when it is nil. This is a common use case for tests where the request
-// is directly passed to the handler.
-func TestHandlerReadingNilBodySuccess(t *testing.T) {
-	h := otelhttp.NewHandler(
-		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if r.Body != nil {
-				_, err := io.ReadAll(r.Body)
-				assert.NoError(t, err)
-			}
-		}), "test_handler",
-	)
-
-	r, err := http.NewRequest(http.MethodGet, "http://localhost/", nil)
-	require.NoError(t, err)
-
-	rr := httptest.NewRecorder()
-	h.ServeHTTP(rr, r)
-	assert.Equal(t, 200, rr.Result().StatusCode)
-}
-
-// This use case is important as we make sure the body isn't mutated
-// when it is NoBody.
-func TestHandlerReadingNoBodySuccess(t *testing.T) {
-	h := otelhttp.NewHandler(
-		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if r.Body != http.NoBody {
-				_, err := io.ReadAll(r.Body)
-				assert.NoError(t, err)
-			}
-		}), "test_handler",
-	)
-
-	r, err := http.NewRequest(http.MethodGet, "http://localhost/", http.NoBody)
-	require.NoError(t, err)
-
-	rr := httptest.NewRecorder()
-	h.ServeHTTP(rr, r)
-	assert.Equal(t, 200, rr.Result().StatusCode)
+			rr := httptest.NewRecorder()
+			tc.handler(t).ServeHTTP(rr, r)
+			assert.Equal(t, tc.expectedStatusCode, rr.Result().StatusCode)
+		})
+	}
 }