Replace assert with JUnit assertions (#648)

* Replace assert with Exception

* Run basic test with experimental Java to reduce false negatives

.github/workflows/maven.yml

@@ -88,7 +88,12 @@ jobs:
         server-username: NEXUS_USER # env variable for username in deploy
         server-password: NEXUS_PW # env variable for token in deploy
     - name: Build with Maven
+      if: ${{ !matrix.experimental }}
       run: mvn --errors --show-version --batch-mode --no-transfer-progress -DtrimStackTrace=false
+    - name: Test only with Maven
+      if: ${{ matrix.experimental }}
+      # Skip PMD etc when using experimental Java
+      run: mvn --errors --show-version --batch-mode --no-transfer-progress -DtrimStackTrace=false clean test
     - name: Deploy SNAPSHOT using minimal build
       if: matrix.deploy && github.repository == 'apache/commons-io' && github.ref_name == 'master' 
       env:

src/main/java/org/apache/commons/io/input/ReadAheadInputStream.java

@@ -485,7 +485,9 @@ public long skip(final long n) throws IOException {
      * @throws IOException if an I/O error occurs.
      */
     private long skipInternal(final long n) throws IOException {
-        assert stateChangeLock.isLocked();
+        if (!stateChangeLock.isLocked()) {
+            throw new IllegalStateException("Expected stateChangeLock to be locked");
+        }
         waitForAsyncReadComplete();
         if (isEndOfStream()) {
             return 0;
@@ -495,7 +497,9 @@ private long skipInternal(final long n) throws IOException {
             int toSkip = (int) n;
             // We need to skip from both active buffer and read ahead buffer
             toSkip -= activeBuffer.remaining();
-            assert toSkip > 0; // skipping from activeBuffer already handled.
+            if (toSkip <= 0) { // skipping from activeBuffer already handled.
+                throw new IllegalStateException("Expected toSkip > 0, actual: " + toSkip);
+            }
             activeBuffer.position(0);
             activeBuffer.flip();
             readAheadBuffer.position(toSkip + readAheadBuffer.position());

src/main/java/org/apache/commons/io/input/ThrottledInputStream.java

@@ -127,7 +127,9 @@ public static Builder builder() {
     }
 
     static long toSleepMillis(final long bytesRead, final long maxBytesPerSec, final long elapsedMillis) {
-        assert elapsedMillis >= 0 : "The elapsed time should be greater or equal to zero";
+        if (elapsedMillis < 0) {
+            throw new IllegalArgumentException("The elapsed time should be greater or equal to zero");
+        }
         if (bytesRead <= 0 || maxBytesPerSec <= 0 || elapsedMillis == 0) {
             return 0;
         }
@@ -147,7 +149,9 @@ static long toSleepMillis(final long bytesRead, final long maxBytesPerSec, final
 
     private ThrottledInputStream(final InputStream proxy, final long maxBytesPerSecond) {
         super(proxy);
-        assert maxBytesPerSecond > 0 : "Bandwidth " + maxBytesPerSecond + " is invalid.";
+        if (maxBytesPerSecond <= 0) {
+            throw new IllegalArgumentException("Bandwidth " + maxBytesPerSecond + " is invalid.");
+        }
         this.maxBytesPerSecond = maxBytesPerSecond;
     }