Android TextView: is there a way to force the marquee animation with short text?

Make your own animation.

anim/marquee.xml

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate
        android:fromXDelta="100%"
        android:toXDelta="-100%"
        android:duration="10000"
        android:repeatCount="infinite"
        android:repeatMode="restart"
        android:interpolator="@android:anim/linear_interpolator"/>
</set>

and in your activity,

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.my_activity);

    TextView myTextView = (TextView) findViewById(R.id.myTextView);
    Animation marquee = AnimationUtils.loadAnimation(this, R.anim.marquee);
    myTextView.startAnimation(marquee);
}

Taking @JodiMiddleton's suggestion about padding the text I constructed a few helper methods to pad the text to a target width based on a TextPaint object (ensuring correct sizing from fonts etc when measuring):

/**
 * Pad a target string of text with spaces on the right to fill a target
 * width
 * 
 * @param text The target text
 * @param paint The TextPaint used to measure the target text and
 *            whitespaces
 * @param width The target width to fill
 * @return the original text with extra padding to fill the width
 */
public static CharSequence padText(CharSequence text, TextPaint paint, int width) {

    // First measure the width of the text itself
    Rect textbounds = new Rect();
    paint.getTextBounds(text.toString(), 0, text.length(), textbounds);

    /**
     * check to see if it does indeed need padding to reach the target width
     */
    if (textbounds.width() > width) {
        return text;
    }

    /*
     * Measure the text of the space character (there's a bug with the
     * 'getTextBounds() method of Paint that trims the white space, thus
     * making it impossible to measure the width of a space without
     * surrounding it in arbitrary characters)
     */
    String workaroundString = "a a";
    Rect spacebounds = new Rect();
    paint.getTextBounds(workaroundString, 0, workaroundString.length(), spacebounds);

    Rect abounds = new Rect();
    paint.getTextBounds(new char[] {
        'a'
    }, 0, 1, abounds);

    float spaceWidth = spacebounds.width() - (abounds.width() * 2);

    /*
     * measure the amount of spaces needed based on the target width to fill
     * (using Math.ceil to ensure the maximum whole number of spaces)
     */
    int amountOfSpacesNeeded = (int)Math.ceil((width - textbounds.width()) / spaceWidth);

    // pad with spaces til the width is less than the text width
    return amountOfSpacesNeeded > 0 ? padRight(text.toString(), text.toString().length()
            + amountOfSpacesNeeded) : text;
}

/**
 * Pads a string with white space on the right of the original string
 * 
 * @param s The target string
 * @param n The new target length of the string
 * @return The target string padded with whitespace on the right to its new
 *         length
 */
public static String padRight(String s, int n) {
    return String.format("%1$-" + n + "s", s);
}

So when you use the methods based on a TextView you would call:

textView.setText(padText(myTargetString, textView.getPaint(), textView.getWidth()));

It's not elegant and I'm almost certain there's improvements that could be made (not to mention a better way of doing it) but nonetheless I'm using it in my code and it appears to be doing the trick :)

I have found a one line code that will do the trick!

Just repeat your short text few times, or separate them with a long blank space.

activity_main.xml

<TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ellipsize="marquee"
        android:focusable="true"
        android:focusableInTouchMode="true"
        android:marqueeRepeatLimit="marquee_forever"
        android:scrollHorizontally="true"
        android:singleLine="true"
        android:text=""
        android:textColor="#ffffff"/>

MainActivity.java

String shortText = "A short text.";
TextView textView = findViewById(R.id.textView);
textView.setText(shortText + "             " + shortText); 
// repeat the above concatenation as many as required 
// just enough to make it marqueeable for auto scrolling 
// or you can just increase the length of the blank space
textView.setSelected(true);