[librptext/tests] TextFuncsTest: Add tests for formatFrequency().

Unlike the file size functions, formatFrequency() works on base 10,
and always has three decimal places once it gets into the kHz range.

librptext code coverage:

Before:
  lines......: 86.7% (424 of 489 lines)
  functions..: 86.5% (32 of 37 functions)

After:
  lines......: 88.5% (433 of 489 lines)
  functions..: 86.5% (32 of 37 functions)

Overall code coverage:

Before:
  lines......: 22.2% (11580 of 52107 lines)
  functions..: 21.3% (773 of 3625 functions)

After:
  lines......: 22.2% (11589 of 52107 lines)
  functions..: 21.3% (773 of 3625 functions)

src/librptext/tests/TextFuncsTest.cpp

@@ -1054,6 +1054,51 @@ TEST_F(TextFuncsTest, formatFileSizeKiB)
 	EXPECT_EQ("4194303 KiB", formatFileSizeKiB(0xFFFFFFFFU));
 }
 
+/**
+ * Test formatFrequency().
+ */
+TEST_F(TextFuncsTest, formatFrequency)
+{
+	// Testing 512, 768, 1024, 1536, 2048, 2560, and 3072 for each order of magnitude.
+	// NOTE: Frequencies aren't powers of two, so the resulting values will
+	// have "weird" decimal points.
+
+	// Special cases
+	EXPECT_EQ("0 Hz", formatFrequency(0U));
+	EXPECT_EQ("1 Hz", formatFrequency(1U));
+	EXPECT_EQ("2 Hz", formatFrequency(2U));
+
+	// Kilohertz
+	EXPECT_EQ("512 Hz", formatFrequency(512U));
+	EXPECT_EQ("768 Hz", formatFrequency(768U));
+	EXPECT_EQ("1024 Hz", formatFrequency(1024U));
+	EXPECT_EQ("1536 Hz", formatFrequency(1536U));
+	EXPECT_EQ("2.048 kHz", formatFrequency(2048U));
+	EXPECT_EQ("2.560 kHz", formatFrequency(2560U));
+	EXPECT_EQ("3.072 kHz", formatFrequency(3072U));
+
+	// Megahertz
+	EXPECT_EQ("524.288 kHz", formatFrequency(512U*1024U));
+	EXPECT_EQ("786.432 kHz", formatFrequency(768U*1024U));
+	EXPECT_EQ("1048.576 kHz", formatFrequency(1024U*1024U));
+	EXPECT_EQ("1572.864 kHz", formatFrequency(1536U*1024U));
+	EXPECT_EQ("2.097 MHz", formatFrequency(2048U*1024U));
+	EXPECT_EQ("2.621 MHz", formatFrequency(2560U*1024U));
+	EXPECT_EQ("3.145 MHz", formatFrequency(3072U*1024U));
+
+	// Gigabyte
+	EXPECT_EQ("536.870 MHz", formatFrequency(512U*1024U*1024U));
+	EXPECT_EQ("805.306 MHz", formatFrequency(768U*1024U*1024U));
+	EXPECT_EQ("1073.741 MHz", formatFrequency(1024U*1024U*1024U));
+	EXPECT_EQ("1610.612 MHz", formatFrequency(1536U*1024U*1024U));
+	EXPECT_EQ("2.147 GHz", formatFrequency(2048U*1024U*1024U));
+	EXPECT_EQ("2.684 GHz", formatFrequency(2560U*1024U*1024U));
+	EXPECT_EQ("3.221 GHz", formatFrequency(3072U*1024U*1024U));
+
+	// Largest value for a 32-bit unsigned integer
+	EXPECT_EQ("4.294 GHz", formatFrequency(0xFFFFFFFFU));
+}
+
 /**
  * Test dos2unix().
  */