Check for inconsistent gauge fields for summaries

lib/build.gradle

@@ -20,7 +20,7 @@ plugins {
 }
 
 group 'com.dynatrace.metric.util'
-version = '2.0.1'
+version = '2.1.0'
 
 repositories {
     mavenCentral()

lib/src/main/java/com/dynatrace/metric/util/MetricLineConstants.java

@@ -73,6 +73,8 @@ private ValidationMessages() {}
     static final String GAUGE_NAN_MESSAGE = "NaN values: min: %f, max %f, sum: %f, count: %d";
     static final String GAUGE_MIN_GREATER_MAX_MESSAGE =
         "max < min: min: %f, max: %f, sum: %f, count: %d";
+    static final String GAUGE_INCONSISTENT_FIELDS_MESSAGE =
+        "inconsistent gauge fields: min <= avg <= max doesn't hold: min: %f, max: %f, sum: %f, count: %d, avg: %f, tolerance: %f";
 
     static final String VALUE_NAN_MESSAGE = "Metric value was NaN";
     static final String VALUE_INFINITE_MESSAGE = "Metric value was infinite (%f)";

lib/src/main/java/com/dynatrace/metric/util/NumberValueValidator.java

@@ -17,6 +17,7 @@
 
 /** Offers validation methods for metric-line values */
 final class NumberValueValidator {
+  private static final double COMPARISON_ABSOLUTE_TOLERANCE = 0.000001D;
 
   private NumberValueValidator() {}
 
@@ -59,9 +60,48 @@ static BooleanResultMessage isSummaryValid(double min, double max, double sum, l
               String.format(
                   ValidationMessages.GAUGE_MIN_GREATER_MAX_MESSAGE, min, max, sum, count));
     }
+
+    double avg = sum / count;
+    if (!(lessOrEqualWithAbsoluteTolerance(min, avg)
+        && lessOrEqualWithAbsoluteTolerance(avg, max))) {
+      // in this case the min <= avg <= max does not hold
+      return BooleanResultMessage.newInvalid(
+          () ->
+              String.format(
+                  ValidationMessages.GAUGE_INCONSISTENT_FIELDS_MESSAGE,
+                  min,
+                  max,
+                  sum,
+                  count,
+                  avg,
+                  COMPARISON_ABSOLUTE_TOLERANCE));
+    }
+
     return BooleanResultMessage.newValid();
   }
 
+  private static boolean lessOrEqualWithAbsoluteTolerance(double val1, double val2) {
+    // equals
+    if (Double.valueOf(val1).equals(Double.valueOf(val2))) {
+      return true;
+    }
+
+    // not equal, two cases:
+    // val1 < val2: should always evaluate to true
+    // val1 slightly < val2 -> val1 - val2 == negative     | result <= tolerance -> true
+    // val1 much < val2 -> val1 - val2 == negative         | result <= tolerance -> true
+    //
+    // val1 > val2: should only evaluate to true if
+    // - val1 is bigger than val2 but within the tolerance:
+    // val1 slightly > val2 -> val1 - val2 == small number | result <= tolerance -> true
+    // val1 much > val2 -> val1 - val2 == larger number    | result > tolerance -> false
+    if ((val1 - val2) <= COMPARISON_ABSOLUTE_TOLERANCE) {
+      return true;
+    }
+
+    return false;
+  }
+
   /**
    * Checks if the value of a gauge or delta of a counter is not a number, or is +/- infinity.
    *

lib/src/test/java/com/dynatrace/metric/util/NumberValueValidatorTest.java

@@ -31,11 +31,33 @@ void testValueValidator() {
     assertFalse(NumberValueValidator.isValueValid(Double.POSITIVE_INFINITY).isValid());
   }
 
+  @Test
+  void testInconsistentGaugeFields() {
+    // min > avg
+    assertFalse(NumberValueValidator.isSummaryValid(2.5, 3, 6, 3).isValid());
+    assertFalse(NumberValueValidator.isSummaryValid(5, 3, 3, 1).isValid());
+    assertFalse(NumberValueValidator.isSummaryValid(-2, -2, -5, 2).isValid());
+
+    // max < avg
+    assertFalse(NumberValueValidator.isSummaryValid(2, 2, 5, 3).isValid());
+    assertFalse(NumberValueValidator.isSummaryValid(10.5, 10.6, 21.3, 1).isValid());
+    assertFalse(NumberValueValidator.isSummaryValid(-5.3, -4.1, -5, 2).isValid());
+
+    // test tolerances (tolerance == 0.000001);
+    // avg == 2; min <= avg does not hold (but is within tolerance).
+    assertTrue(NumberValueValidator.isSummaryValid(2.0000001, 3, 4, 2).isValid());
+    // avg == -2; min <= avg does not hold (but is within tolerance)
+    assertTrue(NumberValueValidator.isSummaryValid(-1.999999, -1, -4, 2).isValid());
+
+    // avg == 2; max >= avg does not hold (but is within tolerance)
+    assertTrue(NumberValueValidator.isSummaryValid(1.5, 1.999999, 4, 2).isValid());
+    // avg == -2; max >= avg does not hold (but is within tolerance)
+    assertTrue(NumberValueValidator.isSummaryValid(-2.5, -2.0000001, -4, 2).isValid());
+  }
+
   @Test
   void testSummaryValidator() {
-    assertTrue(() -> NumberValueValidator.isSummaryValid(10.5, 10.6, 21.3, 1).isValid());
     assertTrue(() -> NumberValueValidator.isSummaryValid(-1.3, 4.1, 5, 2).isValid());
-    assertTrue(() -> NumberValueValidator.isSummaryValid(-5.3, -4.1, -5, 2).isValid());
 
     assertTrue(NumberValueValidator.isSummaryValid(0, 0, 0, 0).isValid());
     assertFalse(NumberValueValidator.isSummaryValid(0, 0, 0, -1).isValid());