fix: XDG_CONFIG_HOME mishandling

Attempts to resolve an issue regarding automatic config file generation,
as referenced in #501. This issue is believed occur when
`XDG_CONFIG_HOME` is unset.

internal/config/paths_test.go

@@ -50,6 +50,47 @@ func TestValidatePathsNix(t *testing.T) {
 	}
 }
 
+// TestValidatePathsNixNoXDG asserts that the proper config paths are returned
+// on *nix platforms when `XDG_CONFIG_HOME is not set
+func TestValidatePathsNixNoXDG(t *testing.T) {
+
+	// mock some envvars
+	envvars := map[string]string{
+		"HOME": "/home/foo",
+	}
+
+	// specify the platforms to test
+	oses := []string{
+		"darwin",
+		"freebsd",
+		"linux",
+	}
+
+	// test each *nix os
+	for _, os := range oses {
+		// get the paths for the platform
+		paths, err := Paths(os, envvars)
+		if err != nil {
+			t.Errorf("paths returned an error: %v", err)
+		}
+
+		// specify the expected output
+		want := []string{
+			"/home/foo/.config/cheat/conf.yml",
+			"/home/foo/.cheat/conf.yml",
+		}
+
+		// assert that output matches expectations
+		if !reflect.DeepEqual(paths, want) {
+			t.Errorf(
+				"failed to return expected paths: want:\n%s, got:\n%s",
+				spew.Sdump(want),
+				spew.Sdump(paths),
+			)
+		}
+	}
+}
+
 // TestValidatePathsWindows asserts that the proper config paths are returned
 // on Windows platforms
 func TestValidatePathsWindows(t *testing.T) {