Address staticcheck issues

Fix `staticcheck` issues:
- S1028 use `fmt.Errorf` to construct formatted errors
- ST1017 yoda conditions
- ST1005 error message capitalization
- ST1006 avoid `self` as receiver name
- S1030 use `buf.String`
- S1011 avoid redundant loop when `append` suffices
- SA4006 unused value
- S1019 remove redundant capacity on `make` call
- SA2002 `t.Fatal` called outside of test

Exported error violates ST1012, which is ignored by this PR since rename may cause breaking changes.

Remove redundant parentheses wrapping, and use CamelCase naming while at it.

ssl_test.go

@@ -197,7 +197,7 @@ func SimpleConnTest(t testing.TB, constructor func(
 		if err != nil {
 			t.Fatal(err)
 		}
-		if string(buf.Bytes()) != data {
+		if buf.String() != data {
 			t.Fatal("mismatched data")
 		}
 
@@ -304,21 +304,21 @@ func ThroughputBenchmark(b *testing.B, constructor func(
 	wg.Add(2)
 	go func() {
 		defer wg.Done()
-		_, err = io.Copy(client, bytes.NewReader([]byte(data)))
-		if err != nil {
-			b.Fatal(err)
+		if _, err = io.Copy(client, bytes.NewReader(data)); err != nil {
+			b.Error(err)
+			return
 		}
 	}()
 	go func() {
 		defer wg.Done()
 
 		buf := &bytes.Buffer{}
-		_, err = io.CopyN(buf, server, int64(len(data)))
-		if err != nil {
-			b.Fatal(err)
+		if _, err = io.CopyN(buf, server, int64(len(data))); err != nil {
+			b.Error(err)
+			return
 		}
 		if !bytes.Equal(buf.Bytes(), data) {
-			b.Fatal("mismatched data")
+			b.Error("mismatched data")
 		}
 	}()
 	wg.Wait()
@@ -551,27 +551,27 @@ func LotsOfConns(t *testing.T, payload_size int64, loops, clients int,
 		for {
 			conn, err := ssl_listener.Accept()
 			if err != nil {
-				t.Fatalf("failed accept: %s", err)
+				t.Errorf("failed accept: %s", err)
 				continue
 			}
 			go func() {
 				defer func() {
 					err = conn.Close()
 					if err != nil {
-						t.Fatalf("failed closing: %s", err)
+						t.Errorf("failed closing: %s", err)
 					}
 				}()
 				for i := 0; i < loops; i++ {
 					_, err := io.Copy(ioutil.Discard,
 						io.LimitReader(conn, payload_size))
 					if err != nil {
-						t.Fatalf("failed reading: %s", err)
+						t.Errorf("failed reading: %s", err)
 						return
 					}
 					_, err = io.Copy(conn, io.LimitReader(rand.Reader,
 						payload_size))
 					if err != nil {
-						t.Fatalf("failed writing: %s", err)
+						t.Errorf("failed writing: %s", err)
 						return
 					}
 				}
@@ -581,35 +581,37 @@ func LotsOfConns(t *testing.T, payload_size int64, loops, clients int,
 	}()
 	var wg sync.WaitGroup
 	for i := 0; i < clients; i++ {
-		tcp_client, err := net.Dial(tcp_listener.Addr().Network(),
+		tcpClient, err := net.Dial(tcp_listener.Addr().Network(),
 			tcp_listener.Addr().String())
 		if err != nil {
-			t.Fatal(err)
+			t.Error(err)
+			return
 		}
-		ssl_client, err := newClient(tcp_client)
+		ssl_client, err := newClient(tcpClient)
 		if err != nil {
-			t.Fatal(err)
+			t.Error(err)
+			return
 		}
 		wg.Add(1)
 		go func(i int) {
+			defer wg.Done()
 			defer func() {
 				err = ssl_client.Close()
 				if err != nil {
-					t.Fatalf("failed closing: %s", err)
+					t.Errorf("failed closing: %s", err)
 				}
-				wg.Done()
 			}()
 			for i := 0; i < loops; i++ {
 				_, err := io.Copy(ssl_client, io.LimitReader(rand.Reader,
 					payload_size))
 				if err != nil {
-					t.Fatalf("failed writing: %s", err)
+					t.Errorf("failed writing: %s", err)
 					return
 				}
 				_, err = io.Copy(ioutil.Discard,
 					io.LimitReader(ssl_client, payload_size))
 				if err != nil {
-					t.Fatalf("failed reading: %s", err)
+					t.Errorf("failed reading: %s", err)
 					return
 				}
 			}
@@ -645,20 +647,17 @@ func TestOpenSSLLotsOfConns(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	err = ctx.UsePrivateKey(key)
-	if err != nil {
+	if err = ctx.UsePrivateKey(key); err != nil {
 		t.Fatal(err)
 	}
 	cert, err := LoadCertificateFromPEM(certBytes)
 	if err != nil {
 		t.Fatal(err)
 	}
-	err = ctx.UseCertificate(cert)
-	if err != nil {
+	if err = ctx.UseCertificate(cert); err != nil {
 		t.Fatal(err)
 	}
-	err = ctx.SetCipherList("AES128-SHA")
-	if err != nil {
+	if err = ctx.SetCipherList("AES128-SHA"); err != nil {
 		t.Fatal(err)
 	}
 	LotsOfConns(t, 1024*64, 10, 100, 0*time.Second,