[Prometheus.Tests] Add tests for mapping metric types (#6645)

Author: Kielek

src/OpenTelemetry.Exporter.Prometheus.HttpListener/Internal/PrometheusMetric.cs

@@ -88,7 +88,7 @@ public PrometheusMetric(string name, string unit, PrometheusType type, bool disa
 
     public static PrometheusMetric Create(Metric metric, bool disableTotalNameSuffixForCounters)
     {
-        return new PrometheusMetric(metric.Name, metric.Unit, GetPrometheusType(metric), disableTotalNameSuffixForCounters);
+        return new PrometheusMetric(metric.Name, metric.Unit, GetPrometheusType(metric.MetricType), disableTotalNameSuffixForCounters);
     }
 
     internal static string SanitizeMetricName(string metricName)
@@ -177,6 +177,12 @@ internal static string RemoveAnnotations(string unit)
         return sb.ToString();
     }
 
+    internal static PrometheusType GetPrometheusType(MetricType openTelemetryMetricType)
+    {
+        int metricType = (int)openTelemetryMetricType >> 4;
+        return MetricTypes[metricType];
+    }
+
     private static string SanitizeOpenMetricsName(string metricName)
     {
         if (metricName.EndsWith("_total", StringComparison.Ordinal))
@@ -231,12 +237,6 @@ private static bool TryProcessRateUnits(string updatedUnit, [NotNullWhen(true)]
         return false;
     }
 
-    private static PrometheusType GetPrometheusType(Metric metric)
-    {
-        int metricType = (int)metric.MetricType >> 4;
-        return MetricTypes[metricType];
-    }
-
     // The map to translate OTLP units to Prometheus units
     // OTLP metrics use the c/s notation as specified at https://ucum.org/ucum.html
     // (See also https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/metrics.md#instrument-units)

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/MetricsMappingTestData.cs

@@ -0,0 +1,21 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+using OpenTelemetry.Metrics;
+
+namespace OpenTelemetry.Exporter.Prometheus.Tests;
+
+#pragma warning disable CA1515 // Consider making public types internal
+public class MetricsMappingTestData
+#pragma warning restore CA1515 // Consider making public types internal
+{
+    internal MetricsMappingTestData(MetricType openTelemetryMetricType, PrometheusType expectedPrometheusType)
+    {
+        this.OpenTelemetryMetricType = openTelemetryMetricType;
+        this.ExpectedPrometheusType = expectedPrometheusType;
+    }
+
+    internal MetricType OpenTelemetryMetricType { get; }
+
+    internal PrometheusType ExpectedPrometheusType { get; }
+}

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests.csproj

@@ -6,6 +6,8 @@
     <DefineConstants>$(DefineConstants);PROMETHEUS_HTTP_LISTENER</DefineConstants>
     <!-- Avoid conflicting port registrations if TFMs tested in parallel -->
     <TestTfmsInParallel>false</TestTfmsInParallel>
+    <!-- CA1062 Validate arguments of public methods - needed for Theory methods -->
+    <NoWarn>$(NoWarn);CA1062</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>

test/OpenTelemetry.Exporter.Prometheus.HttpListener.Tests/PrometheusMetricTests.cs

@@ -1,12 +1,29 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
+using OpenTelemetry.Metrics;
 using Xunit;
 
 namespace OpenTelemetry.Exporter.Prometheus.Tests;
 
 public sealed class PrometheusMetricTests
 {
+    public static TheoryData<MetricsMappingTestData> GetPrometheusType_Data()
+    {
+        var data = new TheoryData<MetricsMappingTestData>
+        {
+            new(MetricType.LongSum, PrometheusType.Counter),
+            new(MetricType.DoubleSum, PrometheusType.Counter),
+            new(MetricType.LongGauge, PrometheusType.Gauge),
+            new(MetricType.DoubleGauge, PrometheusType.Gauge),
+            new(MetricType.Histogram, PrometheusType.Histogram),
+            new(MetricType.ExponentialHistogram, PrometheusType.Histogram),
+            new(MetricType.LongSumNonMonotonic, PrometheusType.Gauge),
+            new(MetricType.DoubleSumNonMonotonic, PrometheusType.Gauge),
+        };
+        return data;
+    }
+
     [Fact]
     public void SanitizeMetricName_Valid()
     {
@@ -247,6 +264,14 @@ public void OpenMetricsMetadataName_Counter_DisableSuffixTotal_NotAppendTotal()
         AssertOpenMetricsMetadataName("db_bytes_written", "By", PrometheusType.Counter, true, "db_bytes_written_bytes");
     }
 
+    [Theory]
+    [MemberData(nameof(GetPrometheusType_Data))]
+    public void GetPrometheusType_MapsOpenTelemetryMetricsTypeToPrometheus(MetricsMappingTestData mappingTestData)
+    {
+        var result = PrometheusMetric.GetPrometheusType(mappingTestData.OpenTelemetryMetricType);
+        Assert.Equal(mappingTestData.ExpectedPrometheusType, result);
+    }
+
     private static void AssertName(
         string name, string unit, PrometheusType type, bool disableTotalNameSuffixForCounters, string expected)
     {