From a31956f3496713a6616032d5b67358742a21133d Mon Sep 17 00:00:00 2001
From: arimu1 <19286898+arimu1@users.noreply.github.com>
Date: Sat, 29 Aug 2026 09:57:57 +0700
Subject: [PATCH] fix: keep EnvironmentVariables buffer in sync during tests

Always update the internal buffer when set/clear is called, including
while a test statement is executing. Previously, changes made during
a test only modified the live environment map, so a later clear() did
not override buffered values from rule configuration and the variable
could reappear when the next test started.

Fixes #86
---
 .../lang/system/EnvironmentVariables.java     |  3 +-
 ...ironmentVariablesClearAcrossTestsTest.java | 82 +++++++++++++++++++
 2 files changed, 83 insertions(+), 2 deletions(-)
 create mode 100644 src/test/java/org/junit/contrib/java/lang/system/EnvironmentVariablesClearAcrossTestsTest.java

diff --git a/src/main/java/org/junit/contrib/java/lang/system/EnvironmentVariables.java b/src/main/java/org/junit/contrib/java/lang/system/EnvironmentVariables.java
index 229cfe19..e88616dd 100644
--- a/src/main/java/org/junit/contrib/java/lang/system/EnvironmentVariables.java
+++ b/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;
 	}
 
diff --git a/src/test/java/org/junit/contrib/java/lang/system/EnvironmentVariablesClearAcrossTestsTest.java b/src/test/java/org/junit/contrib/java/lang/system/EnvironmentVariablesClearAcrossTestsTest.java
new file mode 100644
index 00000000..6855ceaf
--- /dev/null
+++ b/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();
+		}
+	}
+}