Use Java11 constructs for string concatenation.

Author: visumickey

firebase-perf/src/test/java/com/google/firebase/perf/metrics/validator/FirebasePerfTraceValidatorTest.java

@@ -220,25 +220,17 @@ public void traceValidator_customAttributeEmptyKeyAndValue_marksPerfMetricInvali
 
   @Test
   public void traceValidator_customAttributeWithLongKey_marksPerfMetricInvalid() {
-
-    StringBuilder longString = new StringBuilder();
-    for (int i = 0; i <= Constants.MAX_ATTRIBUTE_KEY_LENGTH; i++) {
-      longString.append("a");
-    }
     TraceMetric.Builder trace =
-        createValidTraceMetric().putCustomAttributes(longString.toString(), "value");
+        createValidTraceMetric()
+            .putCustomAttributes("a".repeat(Constants.MAX_ATTRIBUTE_KEY_LENGTH + 1), "value");
     assertThat(new FirebasePerfTraceValidator(trace.build()).isValidPerfMetric()).isFalse();
   }
 
   @Test
   public void traceValidator_customAttributeWithLongValue_marksPerfMetricInvalid() {
-
-    StringBuilder longString = new StringBuilder();
-    for (int i = 0; i <= Constants.MAX_ATTRIBUTE_VALUE_LENGTH; i++) {
-      longString.append("a");
-    }
     TraceMetric.Builder trace =
-        createValidTraceMetric().putCustomAttributes("key", longString.toString());
+        createValidTraceMetric()
+            .putCustomAttributes("key", "a".repeat(Constants.MAX_ATTRIBUTE_VALUE_LENGTH + 1));
     assertThat(new FirebasePerfTraceValidator(trace.build()).isValidPerfMetric()).isFalse();
   }