refact: Adjust tests to conform to project standards

Co-authored-by: Suyash Kumar <suyashkumar2003@gmail.com>

Author: mlibanori

pkg/dicomio/reader_test.go

@@ -3,37 +3,80 @@ package dicomio
 import (
 	"bufio"
 	"encoding/binary"
+	"errors"
+	"io"
 	"strings"
 	"testing"
 )
 
 func TestReader_PeekAtMost(t *testing.T) {
-	buf := bufio.NewReaderSize(strings.NewReader("abcdefghijklmnop"), 16)
-	r := NewReader(buf, binary.LittleEndian, 0)
-
-	if s, err := r.PeekAtMost(3); string(s) != "abc" || err != nil {
-		t.Fatalf("want %q got %q, err=%v", "abc", string(s), err)
+	tests := []struct {
+		name      string
+		data      string
+		peekCount int
+		wantData  string
+		wantErr   error
+	}{
+		{
+			name:      "peek_valid_count_within_buffer",
+			data:      "abcdefghijklmnop",
+			peekCount: 3,
+			wantData:  "abc",
+			wantErr:   nil,
+		},
+		{
+			name:      "peek_zero_bytes",
+			data:      "abcdefghijklmnop",
+			peekCount: 0,
+			wantData:  "",
+			wantErr:   nil,
+		},
+		{
+			name:      "peek_negative_count_returns_error",
+			data:      "abcdefghijklmnop",
+			peekCount: -1,
+			wantData:  "",
+			wantErr:   bufio.ErrNegativeCount,
+		},
+		{
+			name:      "peek_count_larger_than_available_data",
+			data:      "abcdefghijklmnop",
+			peekCount: 32,
+			wantData:  "abcdefghijklmnop",
+			wantErr:   nil,
+		},
 	}
 
-	if s, err := r.PeekAtMost(0); len(s) != 0 || err != nil {
-		t.Fatalf("want %d got %d, err=%v", 0, len(s), err)
-	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := bufio.NewReaderSize(strings.NewReader(tt.data), 16)
+			r := NewReader(buf, binary.LittleEndian, 0)
 
-	if _, err := r.PeekAtMost(-1); err != bufio.ErrNegativeCount {
-		t.Fatalf("want ErrNegativeCount got %v", err)
-	}
+			data, err := r.PeekAtMost(tt.peekCount)
+
+			if !errors.Is(err, tt.wantErr) {
+				t.Errorf("got error %v, want %v", err, tt.wantErr)
+			}
 
-	if s, err := r.PeekAtMost(32); string(s) != "abcdefghijklmnop" || err != nil {
-		t.Fatalf("want %q,  without error, got %q, err=%v", "abcdefghijklmnop", string(s), err)
+			if string(data) != tt.wantData {
+				t.Errorf("got data %q, want %q", string(data), tt.wantData)
+			}
+		})
 	}
+}
+
+func TestReader_PeekAtMost_AfterConsumingAllData(t *testing.T) {
+	buf := bufio.NewReaderSize(strings.NewReader("abcdefghijklmnop"), 16)
+	r := NewReader(buf, binary.LittleEndian, 0)
 
+	// Consume all data
 	n, err := r.in.Read(make([]byte, 16))
 	if n != 16 || err != nil {
-		t.Fatalf("want 16 bytes, without error, got %d bytes, err=%v", n, err)
+		t.Fatalf("failed to consume all data: got %d bytes, err=%v", n, err)
 	}
-
-	if s, err := r.PeekAtMost(1); len(s) == 0 && err == nil {
-		t.Fatalf("want %d got %d, err=%v", 1, len(s), err)
+	// Now try to peek - should return empty slice with EOF error
+	data, err := r.PeekAtMost(1)
+	if len(data) != 0 || !errors.Is(err, io.EOF) {
+		t.Errorf("got len=%d, err=%v, want len=0, err=EOF", len(data), err)
 	}
-
 }