add: reader test ifaces

interfaces/18-testing/reader_test.go

@@ -1,34 +1,48 @@
 package main
 
 import (
-	"io"
+	"io/ioutil"
 	"strings"
 	"testing"
 )
 
-func Test_PNG_Reader_Correct_Signature(t *testing.T) {
-	const input = "\x89PNG\r\n\x1a\nHELLO"
+func TestCorrectSignature(t *testing.T) {
+	const signature = "\x89PNG\r\n\x1a\n"
+	const input = signature + "REST OF THE DATA"
 
-	out, err := readSignature(input)
+	pr := pngReader(strings.NewReader(input))
+
+	out, err := ioutil.ReadAll(pr)
 	if err != nil {
-		t.Fatalf("got: %q; want: <nil> err", err)
+		t.Fatalf("got: %q; want: nil err", err)
 	}
-	if out != input {
-		t.Fatalf("invalid output, got: '%x'; want: '%x'", out, input)
+	if string(out) != input {
+		t.Fatalf("got: % x; want: % x", out, input)
 	}
 }
 
-func Test_PNG_Reader_Incorrect_Signature(t *testing.T) {
-	_, err := readSignature("\x89INCORRECT")
+func TestIncorrectSignature(t *testing.T) {
+	const input = "WITHOUT PNG SIGNATURE"
+
+	// strings.Reader is a read-only, in-memory stream reader.
+	// It's an io.Reader implementation.
+	pr := pngReader(strings.NewReader(input))
+
+	// `ioutil.ReadAll` is a dangerous but useful utility function
+	// that can read all the data from a reader into memory.
+	// Don't use it for large (?) data.
+	_, err := ioutil.ReadAll(pr)
 	if err == nil {
-		t.Fatal("got: nil; want: !nil err")
+		t.Fatalf("got: %v; want: !nil err", err)
 	}
 }
 
-func readSignature(in string) (string, error) {
-	r := strings.NewReader(in)
-	w := strings.Builder{}
-	// _, err := io.Copy(&w, pngReader(r))
-	_, err := io.CopyBuffer(&w, pngReader(r), make([]byte, 1))
-	return w.String(), err
+func TestSummation(t *testing.T) {
+	t.Skip() // skip this test
+
+	result := 1 + 2
+	if result != 5 { // it'll always fail
+		// t.Fatal("want: 5") // not a good error message
+		t.Fatalf("got: %d; want: 5", result) // explanatory error message: good.
+	}
 }