feat: take into account TaskDefs with only TestSelectors.

more information can be found at sbt/junit-interface#108

junit-interface/src/main/java/munit/internal/junitinterface/JUnitRunner.java

@@ -11,8 +11,12 @@
 
 import sbt.testing.Runner;
 import sbt.testing.Task;
+import sbt.testing.Selector;
+import sbt.testing.TestSelector;
 import sbt.testing.TaskDef;
 
+import java.util.stream.Collectors;
+
 final class JUnitRunner implements Runner {
   private final String[] args;
   private final String[] remoteArgs;
@@ -127,7 +131,8 @@ public Task[] tasks(TaskDef[] taskDefs) {
     for (int i = 0; i < length; i++) {
       TaskDef taskDef = taskDefs[i];
       if (shouldRun(computer, taskDef)) {
-        tasks.add(new JUnitTask(this, settings, taskDef, computer));
+        RunSettings alteredSettings = alterRunSettings(this.settings, taskDef.selectors());
+        tasks.add(new JUnitTask(this, alteredSettings, taskDef, computer));
       }
     }
     return tasks.toArray(new Task[0]);
@@ -153,6 +158,30 @@ private RunListener createRunListener(String runListenerClassName) {
     } else return null;
   }
 
+  /**
+   * Alter default RunSettings depending on the passed selectors. If selectors contains only
+   * elements of type TestSelector, then default settings are altered to include only test names
+   * from these selectors. This allows to run particular test cases within given test class.
+   * testFilter is treated as a regular expression, hence joining is done via '|'.
+   */
+  private RunSettings alterRunSettings(RunSettings defaultSettings, Selector[] selectors) {
+    boolean onlyTestSelectors =
+        Arrays.stream(selectors).allMatch(selector -> selector instanceof TestSelector);
+    if (onlyTestSelectors) {
+      String testFilter =
+          Arrays.stream(selectors)
+              .map(selector -> ((TestSelector) selector).testName())
+              .collect(Collectors.joining("|"));
+      // if already provided testFilter is not empty add to it | (regex or operator)
+      String currentFilter =
+          defaultSettings.testFilter.length() > 0 ? defaultSettings.testFilter + "|" : "";
+      String newFilter = currentFilter + testFilter;
+      return defaultSettings.withTestFilter(newFilter);
+    }
+
+    return defaultSettings;
+  }
+
   @Override
   public String done() {
     // Can't simply return the summary due to https://github.com/sbt/sbt/issues/3510

junit-interface/src/main/java/munit/internal/junitinterface/RunSettings.java

@@ -78,6 +78,28 @@ class RunSettings implements Settings {
     this.trimStackTraces = trimStackTraces;
   }
 
+  public RunSettings withTestFilter(String newTestFilter) {
+    String ignoreRunners = String.join(",", this.ignoreRunners);
+    return new RunSettings(
+        this.color,
+        this.decodeScalaNames,
+        this.verbose,
+        this.useSbtLoggers,
+        this.useBufferedLoggers,
+        this.trimStackTraces,
+        this.summary,
+        this.logAssert,
+        ignoreRunners,
+        this.logExceptionClass,
+        this.sysprops,
+        this.globPatterns,
+        this.includeCategories,
+        this.excludeCategories,
+        this.includeTags,
+        this.excludeTags,
+        newTestFilter);
+  }
+
   String decodeName(String name) {
     return decodeScalaNames ? decodeScalaName(name) : name;
   }