tests/sort: add test for default mode

tests/fixtures/sort/default_unsorted_ints.expected

@@ -0,0 +1,100 @@
+1
+10
+100
+11
+12
+13
+14
+15
+16
+17
+18
+19
+2
+20
+21
+22
+23
+24
+25
+26
+27
+28
+29
+3
+30
+31
+32
+33
+34
+35
+36
+37
+38
+39
+4
+40
+41
+42
+43
+44
+45
+46
+47
+48
+49
+5
+50
+51
+52
+53
+54
+55
+56
+57
+58
+59
+6
+60
+61
+62
+63
+64
+65
+66
+67
+68
+69
+7
+70
+71
+72
+73
+74
+75
+76
+77
+78
+79
+8
+80
+81
+82
+83
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+85
+86
+87
+88
+89
+9
+90
+91
+92
+93
+94
+95
+96
+97
+98
+99

tests/fixtures/sort/default_unsorted_ints.txt

@@ -0,0 +1,100 @@
+33
+16
+35
+56
+72
+37
+21
+49
+70
+48
+90
+83
+44
+79
+10
+20
+4
+26
+27
+63
+29
+47
+51
+85
+88
+46
+30
+61
+93
+81
+78
+53
+87
+18
+98
+38
+13
+39
+23
+71
+5
+100
+96
+8
+24
+14
+28
+15
+25
+43
+36
+67
+75
+66
+31
+57
+34
+80
+40
+86
+17
+55
+9
+1
+62
+12
+74
+58
+69
+76
+11
+73
+68
+59
+41
+45
+52
+97
+82
+6
+7
+77
+42
+84
+95
+94
+89
+19
+64
+2
+22
+50
+60
+32
+92
+3
+99
+65
+54
+91

tests/sort.rs

@@ -41,6 +41,11 @@ fn test_month_default() {
     test_helper("month_default", &String::from("-M"));
 }
 
+#[test]
+fn test_default_unsorted_ints() {
+    test_helper("default_unsorted_ints", &String::from(""));
+}
+
 fn test_helper(file_name: &str, args: &String) {
     let (at, mut ucmd) = testing(UTIL_NAME);
     ucmd.arg(args);