Fix float precision issue in coverage diff

plugin/src/main/java/io/jenkins/plugins/coverage/CoverageProcessor.java

@@ -7,6 +7,8 @@
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.io.PrintStream;
+import java.math.BigDecimal;
+import java.math.RoundingMode;
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.ArrayList;
@@ -249,13 +251,12 @@ private Optional<CoverageAction> getPreviousResult(final Run<?, ?> startSearch)
         return Optional.empty();
     }
 
-    private void failBuildIfChangeRequestDecreasedCoverage(final CoverageResult coverageResult, final CoverageAction action)
+    void failBuildIfChangeRequestDecreasedCoverage(final CoverageResult coverageResult, final CoverageAction action)
             throws CoverageException {
         float coverageDiff = coverageResult.getCoverageDelta(CoverageElement.LINE);
-        if (coverageDiff < 0) {
+        if (roundFloat(coverageDiff,2) < 0) {
             String message = "Fail build because this change request decreases line coverage by " + coverageDiff;
             action.setFailMessage(message);
-
             throw new CoverageException(message);
         }
     }
@@ -731,4 +732,7 @@ public static CoverageResult recoverCoverageResult(final Run<?, ?> run) throws I
             return (CoverageResult) ois.readObject();
         }
     }
+    static float roundFloat(final float number, final int scale) {
+       return BigDecimal.valueOf(number).setScale(scale,RoundingMode.DOWN).floatValue();
+    }
 }

plugin/src/test/java/io/jenkins/plugins/coverage/CoverageProcessorTest.java

@@ -0,0 +1,63 @@
+package io.jenkins.plugins.coverage;
+
+import hudson.FilePath;
+import hudson.model.Run;
+import io.jenkins.plugins.coverage.exception.CoverageException;
+import io.jenkins.plugins.coverage.targets.CoverageResult;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+/**
+ * Acceptance tests for CoverageProcessor. Verifies if set options in CoverageProcessor are used and lead to accepted
+ * results.
+ */
+public class CoverageProcessorTest {
+
+    CoverageProcessor coverageProcessor;
+    CoverageResult coverageResult;
+    CoverageAction coverageAction;
+
+    @Before()
+    public void testInit(){
+        coverageProcessor = new CoverageProcessor(mock(Run.class),mock(FilePath.class),null);
+        coverageResult =mock(CoverageResult.class);
+        coverageAction =mock(CoverageAction.class);
+    }
+
+    /**
+     * Test roundFloat method in CoverageProcessor
+     */
+    @Test
+    public void testFloatRounding() {
+        float number=-0.001f;
+        float scaledNumber= CoverageProcessor.roundFloat(number,2);
+        Assert.assertEquals(scaledNumber,0.00,0);
+    }
+
+    @Test()
+    public void testChangeRequestDecreasedCoverageNotFailed_NoChange() throws CoverageException {
+        Mockito.when(coverageResult.getCoverageDelta(any())).thenReturn(-0.001f);
+        //No Exception should be thrown
+        coverageProcessor.failBuildIfChangeRequestDecreasedCoverage(coverageResult,coverageAction);
+        verify(coverageAction, times(0)).setFailMessage(any());
+    }
+
+    @Test(expected = CoverageException.class)
+    public void testChangeRequestDecreasedCoverageFailed_DecCoverage() throws CoverageException {
+        Mockito.when(coverageResult.getCoverageDelta(any())).thenReturn(-1.11f);
+        coverageProcessor.failBuildIfChangeRequestDecreasedCoverage(coverageResult,coverageAction);
+        verify(coverageAction, times(1)).setFailMessage(any());
+    }
+
+    @Test()
+    public void testChangeRequestDecreasedCoverageNotFailed_IncCoverage() throws CoverageException {
+        Mockito.when(coverageResult.getCoverageDelta(any())).thenReturn(0.1f);
+        coverageProcessor.failBuildIfChangeRequestDecreasedCoverage(coverageResult,coverageAction);
+        verify(coverageAction, times(0)).setFailMessage(any());
+    }
+}