fix clippy issues

Author: nyurik

tests/by-util/test_factor.rs

@@ -14,6 +14,7 @@ use uutests::new_ucmd;
 use uutests::util::TestScenario;
 use uutests::util_name;
 
+use std::fmt::Write;
 use std::time::{Duration, SystemTime};
 
 use rand::distr::{Distribution, Uniform};
@@ -55,7 +56,7 @@ fn test_parallel() {
     let n_integers = 100_000;
     let mut input_string = String::new();
     for i in 0..=n_integers {
-        input_string.push_str(&format!("{i} "));
+        let _ = write!(input_string, "{i} ");
     }
 
     let tmp_dir = TempDir::new().unwrap();
@@ -100,7 +101,7 @@ fn test_first_1000_integers() {
     let n_integers = 1000;
     let mut input_string = String::new();
     for i in 0..=n_integers {
-        input_string.push_str(&format!("{i} "));
+        let _ = write!(input_string, "{i} ");
     }
 
     println!("STDIN='{input_string}'");
@@ -124,7 +125,7 @@ fn test_first_1000_integers_with_exponents() {
     let n_integers = 1000;
     let mut input_string = String::new();
     for i in 0..=n_integers {
-        input_string.push_str(&format!("{i} "));
+        let _ = write!(input_string, "{i} ");
     }
 
     println!("STDIN='{input_string}'");
@@ -197,11 +198,11 @@ fn test_random() {
     let mut output_string = String::new();
     for _ in 0..NUM_TESTS {
         let (product, factors) = rand_gt(1 << 63);
-        input_string.push_str(&format!("{product} "));
+        let _ = write!(input_string, "{product} ");
 
-        output_string.push_str(&format!("{product}:"));
+        let _ = write!(output_string, "{product}:");
         for factor in factors {
-            output_string.push_str(&format!(" {factor}"));
+            let _ = write!(output_string, " {factor}");
         }
         output_string.push('\n');
     }
@@ -281,11 +282,11 @@ fn test_random_big() {
     let mut output_string = String::new();
     for _ in 0..NUM_TESTS {
         let (product, factors) = rand_64();
-        input_string.push_str(&format!("{product} "));
+        let _ = write!(input_string, "{product} ");
 
-        output_string.push_str(&format!("{product}:"));
+        let _ = write!(output_string, "{product}:");
         for factor in factors {
-            output_string.push_str(&format!(" {factor}"));
+            let _ = write!(output_string, " {factor}");
         }
         output_string.push('\n');
     }
@@ -298,8 +299,8 @@ fn test_big_primes() {
     let mut input_string = String::new();
     let mut output_string = String::new();
     for prime in PRIMES64 {
-        input_string.push_str(&format!("{prime} "));
-        output_string.push_str(&format!("{prime}: {prime}\n"));
+        let _ = write!(input_string, "{prime} ");
+        let _ = writeln!(output_string, "{prime}: {prime}");
     }
 
     run(input_string.as_bytes(), output_string.as_bytes());
@@ -325,8 +326,8 @@ fn test_primes_with_exponents() {
     let mut output_string = String::new();
     for primes in PRIMES_BY_BITS {
         for &prime in *primes {
-            input_string.push_str(&format!("{prime} "));
-            output_string.push_str(&format!("{prime}: {prime}\n"));
+            let _ = write!(input_string, "{prime} ");
+            let _ = writeln!(output_string, "{prime}: {prime}");
         }
     }