Text: improve and test an assertion.

src/Magnum/Text/AbstractFont.cpp

@@ -309,7 +309,7 @@ AbstractLayouter::AbstractLayouter(UnsignedInt glyphCount): _glyphCount(glyphCou
 AbstractLayouter::~AbstractLayouter() = default;
 
 std::pair<Range2D, Range2D> AbstractLayouter::renderGlyph(const UnsignedInt i, Vector2& cursorPosition, Range2D& rectangle) {
-    CORRADE_ASSERT(i < glyphCount(), "Text::AbstractLayouter::renderGlyph(): glyph index out of bounds", {});
+    CORRADE_ASSERT(i < glyphCount(), "Text::AbstractLayouter::renderGlyph(): index" << i << "out of range for" << glyphCount() << "glyphs", {});
 
     /* Render the glyph */
     Range2D quadPosition, textureCoordinates;

src/Magnum/Text/Test/AbstractLayouterTest.cpp

@@ -23,7 +23,9 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <sstream>
 #include <Corrade/TestSuite/Tester.h>
+#include <Corrade/Utility/DebugStl.h> /** @todo remove once Debug is stream-free */
 
 #include "Magnum/Math/Range.h"
 #include "Magnum/Text/AbstractFont.h"
@@ -34,10 +36,12 @@ struct AbstractLayouterTest: TestSuite::Tester {
     explicit AbstractLayouterTest();
 
     void renderGlyph();
+    void renderGlyphOutOfBounds();
 };
 
 AbstractLayouterTest::AbstractLayouterTest() {
-    addTests({&AbstractLayouterTest::renderGlyph});
+    addTests({&AbstractLayouterTest::renderGlyph,
+              &AbstractLayouterTest::renderGlyphOutOfBounds});
 }
 
 void AbstractLayouterTest::renderGlyph() {
@@ -78,6 +82,22 @@ void AbstractLayouterTest::renderGlyph() {
     CORRADE_COMPARE(rectangle, Range2D({2.0f, 0.5f}, {6.1f, 3.0f}));
 }
 
+void AbstractLayouterTest::renderGlyphOutOfBounds() {
+    struct Layouter: AbstractLayouter {
+        explicit Layouter(): AbstractLayouter{3} {}
+
+        std::tuple<Range2D, Range2D, Vector2> doRenderGlyph(UnsignedInt) override { return {}; }
+    } layouter;
+
+    Range2D rectangle;
+    Vector2 cursorPosition;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    layouter.renderGlyph(3, cursorPosition, rectangle);
+    CORRADE_COMPARE(out.str(), "Text::AbstractLayouter::renderGlyph(): index 3 out of range for 3 glyphs\n");
+}
+
 }}}}
 
 CORRADE_TEST_MAIN(Magnum::Text::Test::AbstractLayouterTest)