Breaking down some more components, adding tests.

* Some bug fixes found during testing/test repair.
* Trying to tease apart the various responsibilities of `metricNamer` into smaller chunks and adding tests for each individual chunk.
* Updating the `provider_test` and `series_registry_test` to fix failures.

pkg/custom-provider/metric_name_converter_test.go

@@ -0,0 +1,85 @@
+package provider
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
+	config "github.com/directxman12/k8s-prometheus-adapter/pkg/config"
+)
+
+func TestWhenNoMappingMetricNameIsUnaltered(t *testing.T) {
+	emptyMapping := config.NameMapping{}
+	RunTest(t, emptyMapping, "my_series", "my_series")
+	RunTest(t, emptyMapping, "your_series", "your_series")
+}
+
+func TestWhenMappingWithOneCaptureGroupMetricNameIsCorrect(t *testing.T) {
+	mapping := config.NameMapping{
+		Matches: "my_(.*)",
+		As:      "your_$1",
+	}
+
+	RunTest(t, mapping, "my_requests_per_second", "your_requests_per_second")
+}
+
+func TestWhenMappingWithMultipleCaptureGroupsMetricNameIsCorrect(t *testing.T) {
+	//ExpandString has some strange behavior when using the $1, $2 syntax
+	//Specifically, it doesn't return the expected values for templates like:
+	//$1_$2
+	//You can work around it by using the ${1} syntax.
+	mapping := config.NameMapping{
+		Matches: "my_([^_]+)_([^_]+)",
+		As:      "your_${1}_is_${2}_large",
+	}
+
+	RunTest(t, mapping, "my_horse_very", "your_horse_is_very_large")
+	RunTest(t, mapping, "my_dog_not", "your_dog_is_not_large")
+}
+
+func TestAsCanBeInferred(t *testing.T) {
+	//When we've got one capture group, we should infer that as the target.
+	mapping := config.NameMapping{
+		Matches: "my_(.+)",
+	}
+
+	RunTest(t, mapping, "my_test_metric", "test_metric")
+
+	//When we have no capture groups, we should infer that the whole thing as the target.
+	mapping = config.NameMapping{
+		Matches: "my_metric",
+	}
+
+	RunTest(t, mapping, "my_metric", "my_metric")
+}
+
+func TestWhenAsCannotBeInferredError(t *testing.T) {
+	//More than one capture group should
+	//result in us giving up on making an educated guess.
+	mapping := config.NameMapping{
+		Matches: "my_([^_]+)_([^_]+)",
+	}
+
+	RunTestExpectingError(t, mapping, "my_horse_very")
+	RunTestExpectingError(t, mapping, "my_dog_not")
+}
+
+func RunTest(t *testing.T, mapping config.NameMapping, input string, expectedResult string) {
+	converter, err := NewMetricNameConverter(mapping)
+	require.NoError(t, err)
+
+	series := prom.Series{
+		Name: input,
+	}
+
+	actualResult, err := converter.GetMetricNameForSeries(series)
+	require.NoError(t, err)
+
+	require.Equal(t, expectedResult, actualResult)
+}
+
+func RunTestExpectingError(t *testing.T, mapping config.NameMapping, input string) {
+	_, err := NewMetricNameConverter(mapping)
+	require.Error(t, err)
+}