Add test for KeyValueResolver

src/test/java/no/digipost/monitoring/micrometer/KeyValueResolverTest.java

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) Posten Norge AS
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package no.digipost.monitoring.micrometer;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.function.BiPredicate;
+import java.util.function.Predicate;
+
+import static java.util.function.Predicate.not;
+import static no.digipost.monitoring.micrometer.KeyValueResolver.FROM_ENVIRONMENT_VARIABLES;
+import static no.digipost.monitoring.micrometer.KeyValueResolver.FROM_SYSTEM_PROPERTIES;
+import static no.digipost.monitoring.micrometer.KeyValueResolver.noValue;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static uk.co.probablyfine.matchers.OptionalMatchers.contains;
+import static uk.co.probablyfine.matchers.OptionalMatchers.empty;
+
+class KeyValueResolverTest {
+
+    private static final String KEY = KeyValueResolverTest.class.getName();
+
+    @Test
+    void resolveFromSystemProperties() {
+        assertThat(KeyValueResolver.FROM_SYSTEM_PROPERTIES.tryResolveValue(KEY), empty());
+        doWithSystemProperty(KEY, "hello",
+                () -> assertThat(KeyValueResolver.FROM_SYSTEM_PROPERTIES.tryResolveValue(KEY), contains("hello")));
+    }
+
+    @Test
+    void resolveFromEnvironmentVariables() {
+        var envVariable = pickAnyExistingEnvironmentVariable();
+        assertThat(KeyValueResolver.FROM_ENVIRONMENT_VARIABLES.tryResolveValue(envVariable.getKey()), contains(envVariable.getValue()));
+    }
+
+    @Test
+    void environmentVariableOverriddenBySystemProperty() {
+        var systemProperties = System.getProperties();
+        var envVariable = pickAnExistingEnvironmentVariable(not(systemProperties::containsKey));
+
+        var resolver = KeyValueResolver.inOrderOfPrecedence(FROM_SYSTEM_PROPERTIES, FROM_ENVIRONMENT_VARIABLES).andThen(Map::entry);
+
+        assertThat(resolver.tryResolveValue(envVariable.getKey()), contains(envVariable));
+
+        doWithSystemProperty(envVariable.getKey(), "overridden",
+                () -> assertThat(resolver.tryResolveValue(envVariable.getKey()), contains(Map.entry(envVariable.getKey(), "overridden"))));
+    }
+
+    @Test
+    void notAbleToResolveAnyValue() {
+        assertThat(KeyValueResolver.inOrderOfPrecedence(noValue(), FROM_SYSTEM_PROPERTIES).tryResolveValue("%&()$# does not exist"), empty());
+    }
+
+
+    private static void doWithSystemProperty(String key, String value, Runnable operation) {
+        try {
+            System.setProperty(key, value);
+            operation.run();
+        } finally {
+            System.clearProperty(key);
+        }
+    }
+
+
+    private static Map.Entry<String, String> pickAnyExistingEnvironmentVariable() {
+        return pickAnExistingEnvironmentVariable(key -> true);
+    }
+
+    private static Map.Entry<String, String> pickAnExistingEnvironmentVariable(Predicate<? super String> keyFilter) {
+        return pickAnExistingEnvironmentVariable((key, value) -> keyFilter.test(key));
+    }
+
+    private static Map.Entry<String, String> pickAnExistingEnvironmentVariable(BiPredicate<? super String, ? super String> keyValueFilter) {
+        var env = System.getenv();
+        return env.entrySet().stream().filter(e -> keyValueFilter.test(e.getKey(), e.getValue())).findAny()
+                .orElseThrow(() -> new NoSuchElementException("Unable to resolve an environment variable from " + env));
+    }
+
+
+}