fix: ensure EnvironmentVariables.clear properly removes variables

src/main/java/org/junit/contrib/java/lang/system/EnvironmentVariables.java

@@ -58,10 +58,9 @@ public class EnvironmentVariables implements TestRule {
 	 * @return the rule itself.
      */
 	public EnvironmentVariables set(String name, String value) {
+		writeVariableToBuffer(name, value);
 		if (statementIsExecuting)
 			writeVariableToEnvMap(name, value);
-		else
-			writeVariableToBuffer(name, value);
 		return this;
 	}
 

src/test/java/org/junit/contrib/java/lang/system/EnvironmentVariablesClearAcrossTestsTest.java

@@ -0,0 +1,82 @@
+package org.junit.contrib.java.lang.system;
+
+import org.junit.Before;
+import org.junit.FixMethodOrder;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.experimental.runners.Enclosed;
+import org.junit.runner.RunWith;
+import org.junit.runners.MethodSorters;
+
+import static java.lang.System.getenv;
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Reproduces <a href="https://github.com/stefanbirkner/system-rules/issues/86">#86</a>.
+ */
+@RunWith(Enclosed.class)
+public class EnvironmentVariablesClearAcrossTestsTest {
+	/**
+	 * Variables set in {@code @Before} can be cleared in one test method without
+	 * being restored from the rule's buffer in later tests.
+	 */
+	@FixMethodOrder(MethodSorters.NAME_ASCENDING)
+	public static class clearInBeforeConfiguredTestClass {
+		@Rule
+		public final EnvironmentVariables environmentVariables = new EnvironmentVariables()
+			.set("someValue", "fromRuleInitializer");
+
+		@Before
+		public void setUp() {
+			environmentVariables.set("someValue", "testLink");
+		}
+
+		@Test
+		public void test01_usesEnvironmentVariableFromBefore() {
+			assertThat(getenv("someValue")).isEqualTo("testLink");
+		}
+
+		@Test
+		public void test02_clearsEnvironmentVariableSetInBefore() {
+			environmentVariables.clear("someValue");
+			assertThat(getenv("someValue")).isNull();
+		}
+
+		@Test
+		public void test03_environmentVariableIsSetAgainAfterClearTest() {
+			assertThat(getenv("someValue")).isEqualTo("testLink");
+		}
+	}
+
+	/**
+	 * The rule instance is shared across tests (same pattern as configuring common
+	 * variables on the rule). Without syncing {@code clear()} to the buffer, a
+	 * variable cleared in one test is restored from the buffer when a later test
+	 * starts.
+	 */
+	@FixMethodOrder(MethodSorters.NAME_ASCENDING)
+	public static class clearedVariableIsNotRestoredFromBuffer {
+		private static final EnvironmentVariables SHARED_ENVIRONMENT_VARIABLES
+			= new EnvironmentVariables().set("someValue", "fromRuleInitializer");
+
+		@Rule
+		public final EnvironmentVariables environmentVariables = SHARED_ENVIRONMENT_VARIABLES;
+
+		@Test
+		public void test01_setVariable() {
+			environmentVariables.set("someValue", "testLink");
+			assertThat(getenv("someValue")).isEqualTo("testLink");
+		}
+
+		@Test
+		public void test02_clearVariable() {
+			environmentVariables.clear("someValue");
+			assertThat(getenv("someValue")).isNull();
+		}
+
+		@Test
+		public void test03_clearedVariableIsNotRestoredFromBuffer() {
+			assertThat(getenv("someValue")).isNull();
+		}
+	}
+}