[JENKINS-31660] avoid reading unnecessary test results from disk

src/main/java/hudson/tasks/junit/CaseResult.java

@@ -402,6 +402,11 @@ public int getPassCount() {
     public int getFailedSince() {
         // If we haven't calculated failedSince yet, and we should,
         // do it now.
+        recomputeFailedSinceIfNeeded();
+        return failedSince;
+    }
+
+    private void recomputeFailedSinceIfNeeded() {
         if (failedSince==0 && getFailCount()==1) {
             CaseResult prev = getPreviousResult();
             if(prev!=null && !prev.isPassed())
@@ -413,9 +418,8 @@ else if (getRun() != null) {
                 // failedSince will be 0, which isn't correct. 
             }
         }
-        return failedSince;
     }
-    
+
     public Run<?,?> getFailedSinceRun() {
     	return getRun().getParent().getBuildByNumber(getFailedSince());
     }
@@ -637,13 +641,7 @@ public void setParentSuiteResult(SuiteResult parent) {
     public void freeze(SuiteResult parent) {
         this.parent = parent;
         // some old test data doesn't have failedSince value set, so for those compute them.
-        if(!isPassed() && failedSince==0) {
-            CaseResult prev = getPreviousResult();
-            if(prev!=null && !prev.isPassed())
-                this.failedSince = prev.failedSince;
-            else
-                this.failedSince = getRun().getNumber();
-        }
+        recomputeFailedSinceIfNeeded();
     }
 
     public int compareTo(CaseResult that) {

src/test/java/hudson/tasks/junit/TestResultLinksTest.java

@@ -30,8 +30,12 @@
 import hudson.model.FreeStyleProject;
 import hudson.model.Result;
 
+import java.io.File;
+import java.io.IOException;
+import java.net.URISyntaxException;
 import java.util.concurrent.TimeUnit;
 
+import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.JenkinsRule;
 import org.jvnet.hudson.test.JenkinsRule.WebClient;
 import org.jvnet.hudson.test.TouchBuilder;
@@ -117,4 +121,20 @@ public void testNonDescendantRelativePath() throws Exception {
         boolean pathStartsWithRootUrl = !pathIsEmptyOrNull && relativePath2.startsWith(rule.jenkins.getRootUrl());
         assertTrue("relative path is empty OR begins with the app root", pathIsEmptyOrNull || pathStartsWithRootUrl ); 
     }
+
+    @Issue("JENKINS-31660")
+    @Test
+    public void testPreviousBuildNotLoaded() throws IOException, URISyntaxException {
+        TestResult testResult = new TestResult();
+        File dataFile = TestResultTest.getDataFile("SKIPPED_MESSAGE/skippedTestResult.xml");
+        testResult.parse(dataFile, null);
+        FreeStyleBuild build = new FreeStyleBuild(project) {
+            @Override
+            public FreeStyleBuild getPreviousBuild() {
+                fail("When no tests fail, we don't need tp load previous builds (expensive)");
+                return null;
+            }
+        };
+        testResult.freeze(new TestResultAction(build, testResult, null));
+     }
 }

src/test/java/hudson/tasks/junit/TestResultTest.java

@@ -50,7 +50,7 @@
  * @author dty
  */
 public class TestResultTest {
-    private File getDataFile(String name) throws URISyntaxException {
+    protected static File getDataFile(String name) throws URISyntaxException {
         return new File(TestResultTest.class.getResource(name).toURI());
     }