test: enforce 100% runtime line coverage

.github/workflows/build.yml

@@ -66,3 +66,11 @@ jobs:
           name: unit-test-reports-${{ github.run_id }}-${{ github.run_attempt }}
           path: target/surefire-reports/
           if-no-files-found: error
+
+      - name: Upload coverage report
+        if: ${{ !cancelled() && hashFiles('target/site/jacoco/jacoco.xml') != '' }}
+        uses: actions/upload-artifact@v7
+        with:
+          name: coverage-report-${{ github.run_id }}-${{ github.run_attempt }}
+          path: target/site/jacoco/
+          if-no-files-found: error

README.md

@@ -22,6 +22,15 @@ Returning to the safe area clears the warning, keeping the border feedback tied
 
 Technical documentation is maintained in [TF-Minecraft/Docs](https://github.com/TF-Minecraft/Docs).
 
+## Tests and coverage
+
+Run `mvn clean verify` with Java 21 and the pinned plugin dependencies installed.
+The build runs the tests and enforces **100% executable-line coverage** across
+all production Java classes, with no coverage exclusions. JaCoCo's HTML and XML
+reports are written to `target/site/jacoco/` and uploaded by the Build workflow.
+Branch and instruction coverage are reported separately; the enforced threshold
+is line coverage. Build and maintenance scripts are outside this runtime-code metric.
+
 ## License
 
 Copyright (c) 2026 TF-Minecraft contributors.

pom.xml

@@ -12,9 +12,28 @@
         <maven.compiler.release>21</maven.compiler.release>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.proc>full</maven.compiler.proc>
+        <argLine></argLine>
     </properties>
 
     <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.14.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>5.23.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockbukkit.mockbukkit</groupId>
+            <artifactId>mockbukkit-v1.21</artifactId>
+            <version>4.95.0</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>io.papermc.paper</groupId>
             <artifactId>paper-api</artifactId>
@@ -48,6 +67,55 @@
             </resource>
         </resources>
         <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <version>3.7.0</version>
+                <executions>
+                    <execution><goals><goal>properties</goal></goals></execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>3.5.4</version>
+                <configuration>
+                    <argLine>@{argLine} -javaagent:${org.mockito:mockito-core:jar} -Xshare:off</argLine>
+                    <failIfNoTests>true</failIfNoTests>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.jacoco</groupId>
+                <artifactId>jacoco-maven-plugin</artifactId>
+                <version>0.8.15</version>
+                <executions>
+                    <execution><goals><goal>prepare-agent</goal></goals></execution>
+                    <execution>
+                        <id>coverage-report</id>
+                        <phase>verify</phase>
+                        <goals><goal>report</goal></goals>
+                    </execution>
+                    <execution>
+                        <id>coverage-check</id>
+                        <phase>verify</phase>
+                        <goals><goal>check</goal></goals>
+                        <configuration>
+                            <rules>
+                                <rule>
+                                    <element>BUNDLE</element>
+                                    <limits>
+                                        <limit>
+                                            <counter>LINE</counter>
+                                            <value>MISSEDCOUNT</value>
+                                            <maximum>0</maximum>
+                                        </limit>
+                                    </limits>
+                                </rule>
+                            </rules>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>

src/test/java/net/tfminecraft/worldborder/WorldBorderTest.java

@@ -0,0 +1,117 @@
+package net.tfminecraft.worldborder;
+
+import net.tfminecraft.worldborder.cache.Cache;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.mockbukkit.mockbukkit.MockBukkit;
+import org.mockbukkit.mockbukkit.ServerMock;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.logging.Logger;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.contains;
+import static org.mockito.Mockito.*;
+
+class WorldBorderTest {
+    @TempDir Path directory;
+    private ServerMock server;
+    private WorldBorder plugin;
+
+    @BeforeEach
+    void setUp() {
+        Cache.worlds = new ArrayList<>();
+        Cache.borders = new LinkedHashMap<>();
+        Cache.tickIntervalTicks = 10;
+        Cache.damage = 8.0;
+        Cache.graceInset = 20;
+        Cache.titleWarning = "§cTurn back";
+        Cache.subtitleWarning = "§cYou feel continuing further would be very dangerous...";
+        server = MockBukkit.mock();
+        plugin = MockBukkit.load(WorldBorder.class);
+    }
+
+    @AfterEach
+    void tearDown() {
+        MockBukkit.unmock();
+        WorldBorder.plugin = null;
+        Cache.worlds = new ArrayList<>();
+        Cache.borders = new LinkedHashMap<>();
+    }
+
+    @Test
+    void enablesWithBundledConfigAndCommand() {
+        assertSame(plugin, WorldBorder.plugin);
+        assertTrue(Files.isRegularFile(plugin.getDataFolder().toPath().resolve("config.yml")));
+        assertEquals(10, Cache.tickIntervalTicks);
+        assertEquals(8.0, Cache.damage);
+        assertNotNull(plugin.getCommand("worldborder").getExecutor());
+        assertSame(plugin.getCommand("worldborder").getExecutor(),
+                plugin.getCommand("worldborder").getTabCompleter());
+        server.getScheduler().performTicks(10);
+    }
+
+    @Test
+    void reloadsExistingConfigWithoutReplacingIt() throws Exception {
+        Path config = plugin.getDataFolder().toPath().resolve("config.yml");
+        String custom = "tick-interval-ticks: 5\ndamage: 3\nborders: {}\n";
+        Files.writeString(config, custom);
+        plugin.reloadAll();
+        assertEquals(5, Cache.tickIntervalTicks);
+        assertEquals(3, Cache.damage);
+        plugin.onEnable();
+        assertEquals(custom, Files.readString(config));
+        plugin.onDisable();
+        plugin.onDisable();
+    }
+
+    @Test
+    void createsDataDirectoryAndReportsMissingCommand() throws Exception {
+        WorldBorder controlled = spy(plugin);
+        Path data = directory.resolve("new-data");
+        doReturn(data.toFile()).when(controlled).getDataFolder();
+        doReturn(null).when(controlled).getCommand("worldborder");
+        Logger logger = mock(Logger.class);
+        doReturn(logger).when(controlled).getLogger();
+        controlled.onEnable();
+        assertTrue(Files.isRegularFile(data.resolve("config.yml")));
+        verify(logger).severe("Command 'worldborder' missing from plugin.yml");
+        controlled.onDisable();
+    }
+
+    @Test
+    void reportsMissingBundledResource() {
+        WorldBorder controlled = spy(plugin);
+        doReturn(directory.toFile()).when(controlled).getDataFolder();
+        doReturn(null).when(controlled).getResource("config.yml");
+        Logger logger = mock(Logger.class);
+        doReturn(logger).when(controlled).getLogger();
+        controlled.onEnable();
+        assertFalse(Files.exists(directory.resolve("config.yml")));
+        verify(logger).warning("Missing bundled resource: config.yml");
+        verify(logger).severe(contains("Failed to load config.yml:"));
+        controlled.onDisable();
+    }
+
+    @Test
+    void reportsResourceReadFailureAndClosesItsStream() throws Exception {
+        WorldBorder controlled = spy(plugin);
+        doReturn(directory.toFile()).when(controlled).getDataFolder();
+        InputStream broken = mock(InputStream.class);
+        when(broken.transferTo(any())).thenThrow(new IOException("read failed"));
+        doReturn(broken).when(controlled).getResource("config.yml");
+        Logger logger = mock(Logger.class);
+        doReturn(logger).when(controlled).getLogger();
+        controlled.onEnable();
+        verify(logger).severe("Failed to copy default resource config.yml: read failed");
+        verify(broken).close();
+        controlled.onDisable();
+    }
+}