Matrix: add proper print function testing

Before the print function was just implicitly called somewhere
and that's why we had 100% line coverage. With this we have actual
testing of the functions.

matrix/Matrix.hpp

@@ -322,18 +322,19 @@ public:
         const Matrix<Type, M, N> &self = *this;
         for (size_t i = 0; i < M; i++) {
             for (size_t j = 0; j < N; j++) {
-                snprintf(buf + strlen(buf), n - strlen(buf), "\t%8.2g", double(self(i, j))); // directly append to the string buffer
+                snprintf(buf + strlen(buf), n - strlen(buf), "\t%8.8g", double(self(i, j))); // directly append to the string buffer
             }
             snprintf(buf + strlen(buf), n - strlen(buf), "\n");
         }
     }
 
-    void print() const
+    void print(FILE *stream = stdout) const
     {
-        static const size_t n = 11*N*M + M; // for every entry a tab and 10 digits, for every row a newline
+        // element: tab, point, 8 digits; row: newline; string: \0 end
+        static const size_t n = 10*N*M + M + 1;
         char * buf = new char[n];
         write_string(buf, n);
-        printf("%s\n", buf);
+        fprintf(stream, "%s\n", buf);
         delete[] buf;
     }
 

test/matrixAssignment.cpp

@@ -132,6 +132,44 @@ int main()
     m7.setNaN();
     TEST(m7 != m8);
 
+    // check write_string()
+    float comma[6] = {
+        1.f, 12345.678f,
+        12345.67891f, 12345.67891f,
+        1112345.67891f, 12345.111111111f
+    };
+    Matrix<float, 3, 2> Comma(comma);
+    const size_t len = 10*2*3 + 2 + 1;
+    char buffer[len];
+    Comma.write_string(buffer, len);
+    char output[] = "\t       1\t12345.678\n\t12345.679\t12345.679\n\t1112345.6\t12345.111\n";
+    for (size_t i = 0; i < len; i++) {
+        TEST(buffer[i] == output[i]);
+        if (buffer[i] == '\0') {
+            break;
+        }
+    }
+
+    // check print()
+    // write
+    FILE *fp = fopen("testoutput.txt", "w+");
+    TEST(fp != nullptr);
+    Comma.print(fp);
+    TEST(!fclose(fp));
+    // read
+    fp = fopen("testoutput.txt", "r");
+    TEST(fp != nullptr);
+    TEST(!fseek(fp, 0, SEEK_SET));
+    for (size_t i = 0; i < len; i++) {
+        char c = static_cast<char>(fgetc(fp));
+        if (c == '\n') {
+            break;
+        }
+        printf("%d %d %c\n", static_cast<int>(i), c, c);
+        TEST(c == output[i]);
+    }
+    TEST(!fclose(fp));
+
     return 0;
 }